VoidType: Add tests and fix some bugs

This was a tricky one. In order to call malloc the stack needs to be 16 byte aligned. GenASM up until this point was 8 byte aligned. This commit changes the code generation so that it is guaranteed that the stack is 16 byte aligned before visiting a child node. We need to do this before visiting *any* child node because we can not know whether somewhere downstream some child node calls malloc.

To make it possible for a visitor method to determine if it needs to align the stack it has to assume that the stack is currently aligned. This is the other reason we ensure that the stack is aligned before visiting any child node.

On top of that some visitor methods did not clean up after themselves. I am not sure why this did not result in segfaults already, but I changed the code so that each visitor method leaves the stack in the same state after completion.

.gitignore

@@ -16,4 +16,5 @@ src/main/antlr4/de/hsrm/compiler/Klang/.antlr
 
 # build output
 out
-src/test/test
+src/test/test
+/.idea/uiDesigner.xml

.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/compiler.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <annotationProcessing>
+      <profile name="Maven default annotation processors profile" enabled="true">
+        <sourceOutputDir name="target/generated-sources/annotations" />
+        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
+        <outputRelativeToContentRoot value="true" />
+        <module name="klang" />
+      </profile>
+    </annotationProcessing>
+    <bytecodeTargetLevel>
+      <module name="klang" target="17" />
+    </bytecodeTargetLevel>
+  </component>
+</project>

.idea/encodings.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/target/generated-sources/antlr4" charset="UTF-8" />
+  </component>
+</project>

.idea/jarRepositories.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RemoteRepositoriesConfiguration">
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Central Repository" />
+      <option name="url" value="https://repo.maven.apache.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Maven Central repository" />
+      <option name="url" value="https://repo1.maven.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="jboss.community" />
+      <option name="name" value="JBoss Community repository" />
+      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
+    </remote-repository>
+  </component>
+</project>

.idea/libraries/Maven__org_antlr_antlr4_runtime_4_7_2.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.antlr:antlr4-runtime:4.7.2">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/antlr/antlr4-runtime/4.7.2/antlr4-runtime-4.7.2.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/antlr/antlr4-runtime/4.7.2/antlr4-runtime-4.7.2-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/antlr/antlr4-runtime/4.7.2/antlr4-runtime-4.7.2-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_apiguardian_apiguardian_api_1_1_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.apiguardian:apiguardian-api:1.1.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/apiguardian/apiguardian-api/1.1.0/apiguardian-api-1.1.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/apiguardian/apiguardian-api/1.1.0/apiguardian-api-1.1.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/apiguardian/apiguardian-api/1.1.0/apiguardian-api-1.1.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_junit_jupiter_junit_jupiter_api_5_6_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.junit.jupiter:junit-jupiter-api:5.6.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-api/5.6.0/junit-jupiter-api-5.6.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-api/5.6.0/junit-jupiter-api-5.6.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-api/5.6.0/junit-jupiter-api-5.6.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_junit_jupiter_junit_jupiter_engine_5_6_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.junit.jupiter:junit-jupiter-engine:5.6.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-engine/5.6.0/junit-jupiter-engine-5.6.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-engine/5.6.0/junit-jupiter-engine-5.6.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-engine/5.6.0/junit-jupiter-engine-5.6.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_junit_platform_junit_platform_commons_1_6_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.junit.platform:junit-platform-commons:1.6.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-commons/1.6.0/junit-platform-commons-1.6.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-commons/1.6.0/junit-platform-commons-1.6.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-commons/1.6.0/junit-platform-commons-1.6.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_junit_platform_junit_platform_engine_1_6_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.junit.platform:junit-platform-engine:1.6.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-engine/1.6.0/junit-platform-engine-1.6.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-engine/1.6.0/junit-platform-engine-1.6.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-engine/1.6.0/junit-platform-engine-1.6.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/libraries/Maven__org_opentest4j_opentest4j_1_2_0.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.opentest4j:opentest4j:1.2.0">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/opentest4j/opentest4j/1.2.0/opentest4j-1.2.0.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/opentest4j/opentest4j/1.2.0/opentest4j-1.2.0-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/opentest4j/opentest4j/1.2.0/opentest4j-1.2.0-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

.idea/misc.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ANTLRGenerationPreferences">
+    <option name="perGrammarGenerationSettings">
+      <list>
+        <PerGrammarGenerationSettings>
+          <option name="fileName" value="$PROJECT_DIR$/src/main/antlr4/de/hsrm/compiler/Klang/Klang.g4" />
+          <option name="outputDir" value="" />
+          <option name="libDir" value="" />
+          <option name="encoding" value="" />
+          <option name="pkg" value="" />
+          <option name="language" value="" />
+          <option name="generateVisitor" value="true" />
+        </PerGrammarGenerationSettings>
+      </list>
+    </option>
+  </component>
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="corretto-17" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/classes" />
+  </component>
+</project>

.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/klang.iml" filepath="$PROJECT_DIR$/klang.iml" />
+    </modules>
+  </component>
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>

klang.iml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module org.jetbrains.idea.maven.project.MavenProjectsManager.isMavenModule="true" type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" LANGUAGE_LEVEL="JDK_17">
+    <output url="file://$MODULE_DIR$/target/classes" />
+    <output-test url="file://$MODULE_DIR$/target/test-classes" />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src/main/java" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/target/generated-sources/antlr4" isTestSource="false" generated="true" />
+      <excludeFolder url="file://$MODULE_DIR$/target" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="Maven: org.antlr:antlr4-runtime:4.7.2" level="project" />
+    <orderEntry type="library" name="Maven: org.junit.jupiter:junit-jupiter-api:5.6.0" level="project" />
+    <orderEntry type="library" name="Maven: org.apiguardian:apiguardian-api:1.1.0" level="project" />
+    <orderEntry type="library" name="Maven: org.opentest4j:opentest4j:1.2.0" level="project" />
+    <orderEntry type="library" name="Maven: org.junit.platform:junit-platform-commons:1.6.0" level="project" />
+    <orderEntry type="library" name="Maven: org.junit.jupiter:junit-jupiter-engine:5.6.0" level="project" />
+    <orderEntry type="library" name="Maven: org.junit.platform:junit-platform-engine:1.6.0" level="project" />
+  </component>
+</module>

pom.xml

@@ -40,7 +40,7 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.8.0</version>
         <configuration>
-          <release>11</release>
+          <release>17</release>
         </configuration>
       </plugin>
       <!-- Plugin to compile the g4 files ahead of the java files
@@ -72,6 +72,11 @@
           <descriptorRefs>
             <descriptorRef>jar-with-dependencies</descriptorRef>
           </descriptorRefs>
+          <archive>
+            <manifest>
+              <mainClass>de.hsrm.compiler.Klang.Klang</mainClass>
+            </manifest>
+          </archive>
         </configuration>
         <executions>
           <execution>

src/main/antlr4/de/hsrm/compiler/Klang/Klang.g4

@@ -5,7 +5,11 @@ parse
   ;
 
 program
-  : (functionDef | structDef)* expression SCOL
+  : (functionDef | structDef | enumDef)* expression SCOL
+  ;
+
+enumDef
+  : ENUM enumName=IDENT OBRK (IDENT (COMMA IDENT)*)+ CBRK
   ;
 
 structDef
@@ -29,7 +33,7 @@ parameter
   ;
 
 braced_block
-  : OBRK statement+ CBRK
+  : OBRK (statement | functionCall SCOL)+ CBRK
   ;
 
 
@@ -69,7 +73,7 @@ field_assignment
   ;
 
 return_statement
-  : RETURN expression SCOL
+  : RETURN expression? SCOL
   ;
 
 destroy_statement
@@ -78,7 +82,7 @@ destroy_statement
 
 expression
   : atom #atomExpression
-  | IDENT (PERIOD IDENT)+ #structFieldAccessExpression
+  | IDENT (PERIOD IDENT)+ #memberAccessExpression
   | OPAR expression CPAR #parenthesisExpression
   | lhs=expression MUL rhs=expression #multiplicationExpression
   | lhs=expression DIV rhs=expression #divisionExpression
@@ -116,6 +120,7 @@ type
   | BOOLEAN
   | FLOAT
   | IDENT
+  | VOID
   ;
 
 functionCall
@@ -143,6 +148,7 @@ forLoop
 IF: 'if';
 ELSE: 'else';
 FUNC: 'function';
+ENUM: 'enum';
 STRUCT: 'struct';
 RETURN: 'return';
 LET: 'let';
@@ -181,6 +187,7 @@ DIV: '/';
 BOOLEAN: 'bool';
 INTEGER: 'int';
 FLOAT: 'float';
+VOID: 'void';
 
 INTEGER_LITERAL
   : [0-9]+

src/main/java/de/hsrm/compiler/Klang/ContextAnalysis.java

@@ -1,9 +1,5 @@
 package de.hsrm.compiler.Klang;
 
-import java.util.Map;
-import java.util.HashMap;
-
-import de.hsrm.compiler.Klang.helper.FunctionInformation;
 import de.hsrm.compiler.Klang.helper.Helper;
 import de.hsrm.compiler.Klang.nodes.*;
 import de.hsrm.compiler.Klang.nodes.expressions.*;
@@ -12,11 +8,16 @@ import de.hsrm.compiler.Klang.nodes.loops.ForLoop;
 import de.hsrm.compiler.Klang.nodes.loops.WhileLoop;
 import de.hsrm.compiler.Klang.nodes.statements.*;
 import de.hsrm.compiler.Klang.types.Type;
+import org.antlr.v4.runtime.tree.TerminalNode;
+
+import java.util.*;
 
 public class ContextAnalysis extends KlangBaseVisitor<Node> {
+  Map<String, VariableDeclaration> params = new HashMap<>();
   Map<String, VariableDeclaration> vars = new HashMap<>();
-  Map<String, FunctionInformation> funcs;
-  Map<String, StructDefinition> structs;
+  Map<String, FunctionDefinition> functionDefs;
+  Map<String, StructDefinition> structDefs;
+  Map<String, EnumDefinition> enumDefs;
   Type currentDeclaredReturnType;
   String currentFunctionDefinitionName;
 
@@ -27,25 +28,35 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     }
   }
 
-  public ContextAnalysis(Map<String, FunctionInformation> funcs, Map<String, StructDefinition> structs) {
-    this.funcs = funcs;
-    this.structs = structs;
+  public ContextAnalysis(
+          Map<String, FunctionDefinition> functionDefs,
+          Map<String, StructDefinition> structDefs,
+          Map<String, EnumDefinition> enumDefs
+  ) {
+    this.functionDefs = functionDefs;
+    this.structDefs = structDefs;
+    this.enumDefs = enumDefs;
   }
 
   @Override
   public Node visitProgram(KlangParser.ProgramContext ctx) {
-    FunctionDefinition[] funcs = new FunctionDefinition[ctx.functionDef().size()];
+    var typeCheckedFunctionDefs = new FunctionDefinition[ctx.functionDef().size()];
+    var typeCheckedStructDefs = new HashMap<String, StructDefinition>();
 
     for (int i = 0; i < ctx.functionDef().size(); i++) {
-      funcs[i] = (FunctionDefinition) this.visit(ctx.functionDef(i));
+      typeCheckedFunctionDefs[i] = (FunctionDefinition) visit(ctx.functionDef(i));
     }
 
-    Expression expression = (Expression) this.visit(ctx.expression());
-    Program result = new Program(funcs, this.structs, expression);
-    result.type = expression.type;
-    result.line = ctx.start.getLine();
-    result.col = ctx.start.getCharPositionInLine();
-    return result;
+    for (int i = 0; i < ctx.structDef().size(); i++) {
+      typeCheckedStructDefs.put(ctx.structDef(i).structName.getText(), (StructDefinition) visit(ctx.structDef(i)));
+    }
+
+    var expression = (Expression) visit(ctx.expression());
+    var program = new Program(typeCheckedFunctionDefs, typeCheckedStructDefs, enumDefs, expression);
+    program.type = expression.type;
+    program.line = ctx.start.getLine();
+    program.col = ctx.start.getCharPositionInLine();
+    return program;
   }
 
   @Override
@@ -57,22 +68,22 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitBraced_block(KlangParser.Braced_blockContext ctx) {
-    int actualStatementCount = 0;
-    int declaredStatementCount = ctx.statement().size();
-    boolean hasReturn = false;
-    Statement[] statements = new Statement[declaredStatementCount];
+    var actualStatementCount = 0;
+    var declaredStatementCount = ctx.statement().size();
+    var hasReturn = false;
+    var statements = new Statement[declaredStatementCount];
 
     for (int i = 0; i < declaredStatementCount; i++) {
-      Node currentStatement = this.visit(ctx.statement(i));
+      var currentStatement = visit(ctx.statement(i));
       statements[i] = (Statement) currentStatement;
       actualStatementCount += 1;
 
-      // We use the existance of a type to indicate that this statement returns
+      // We use the existence of a type to indicate that this statement returns
       // something for which the VariableDeclaration is an exception
       if (currentStatement.type != null && !(currentStatement instanceof VariableDeclaration)) {
         // check whether the type matches
         try {
-          this.currentDeclaredReturnType.combine(currentStatement.type);
+          currentDeclaredReturnType.combine(currentStatement.type);
         } catch (Exception e) {
           throw new RuntimeException(
               Helper.getErrorPrefix(currentStatement.line, currentStatement.col) + e.getMessage());
@@ -88,16 +99,15 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     // If there was unreachable code in this block,
     // create a shorter statements array and copy the statements to there
     if (actualStatementCount < declaredStatementCount) {
-      Statement[] newStatements = new Statement[actualStatementCount];
-      for (int i = 0; i < actualStatementCount; i++) {
-        newStatements[i] = statements[i];
-      }
+      var newStatements = new Statement[actualStatementCount];
+      System.arraycopy(statements, 0, newStatements, 0, actualStatementCount);
       statements = newStatements;
     }
 
     // if this block contains at least one statement that guarantees a return value,
     // we indicate that this block guarantees a return value by setting result.type
-    Block result = new Block(statements);
+    var result = new Block(statements);
+
     if (hasReturn) {
       result.type = this.currentDeclaredReturnType;
     }
@@ -172,72 +182,89 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitVariable_declaration(KlangParser.Variable_declarationContext ctx) {
-    String name = ctx.IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    Type declaredType = Type.getByName(ctx.type_annotation().type().getText());
+    var variableName = ctx.IDENT().getText();
+    var declaredType = Type.getByName(ctx.type_annotation().type().getText());
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    if (!declaredType.isPrimitiveType() && this.structs.get(declaredType.getName()) == null) {
-      String error = "Type " + declaredType.getName() + " not defined.";
+    if (declaredType.equals(Type.getVoidType())) {
+      var error = "Type " + declaredType.getName() + " can not be used to declare variables.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    if (this.vars.get(name) != null) {
-      String error = "Redeclaration of variable with name \"" + name + "\".";
+    if (!declaredType.isPrimitiveType() && !structDefs.containsKey(declaredType.getName()) && !enumDefs.containsKey(declaredType.getName())) {
+      var error = "Type " + declaredType.getName() + " not defined.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (structDefs.containsKey(variableName)) {
+      var error = "Variable name " + variableName + " shadows a struct of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (enumDefs.containsKey(variableName)) {
+      var error = "Variable name " + variableName + " shadows an enum of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (vars.get(variableName) != null || params.get(variableName) != null) {
+      var error = "Redeclaration of variable or parameter with name \"" + variableName + "\".";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
     // Create the appropriate instance
-    VariableDeclaration result;
+    VariableDeclaration variableDeclaration;
     if (ctx.expression() != null) {
-      Node expression = this.visit(ctx.expression());
+      var expression = visit(ctx.expression());
       try {
         declaredType.combine(expression.type);
       } catch (Exception e) {
         throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
       }
-      result = new VariableDeclaration(name, (Expression) expression);
-      result.initialized = true;
+      variableDeclaration = new VariableDeclaration(variableName, (Expression) expression);
+      variableDeclaration.initialized = true;
     } else {
-      result = new VariableDeclaration(name);
+      if (enumDefs.containsKey(declaredType.getName())) {
+        var error = "Variable " + variableName + " references an enum but is not initialized.";
+        throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+      }
+
+      variableDeclaration = new VariableDeclaration(variableName);
     }
 
     // Add it to the global map of variable declarations
-    this.vars.put(name, result);
+    vars.put(variableName, variableDeclaration);
 
-    result.line = line;
-    result.col = col;
-    result.type = declaredType;
-    return result;
+    variableDeclaration.line = line;
+    variableDeclaration.col = col;
+    variableDeclaration.type = declaredType;
+
+    return variableDeclaration;
   }
 
   @Override
   public Node visitVariable_assignment(KlangParser.Variable_assignmentContext ctx) {
-    String name = ctx.IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var name = ctx.IDENT().getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    VariableDeclaration var = this.vars.get(name);
-    if (var == null) {
-      String error = "Variable with name \"" + name + "\" not defined.";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
+    var variableOrParameter = getVariableOrParameter(name, line, col);
 
     // Evaluate the expression
-    Expression expression = (Expression) this.visit(ctx.expression());
+    var expression = (Expression) visit(ctx.expression());
 
     // Make sure expression can be assigned to the variable
     try {
-      expression.type.combine(var.type);
+      expression.type.combine(variableOrParameter.type);
     } catch (Exception e) {
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
     }
 
     // Since we assigned a value to this variable, we can consider it initialized
-    var.initialized = true;
+    variableOrParameter.initialized = true;
 
     // Create a new node and add the type of the expression to it
-    Node result = new VariableAssignment(name, expression);
+    var result = new VariableAssignment(name, expression);
     result.line = line;
     result.col = col;
     return result;
@@ -245,109 +272,102 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitReturn_statement(KlangParser.Return_statementContext ctx) {
-    Expression expression = (Expression) this.visit(ctx.expression());
-    ReturnStatement result = new ReturnStatement(expression);
+    if (currentDeclaredReturnType.equals(Type.getVoidType())) {
+      var result = new ReturnStatement();
+      result.type = Type.getVoidType();
+      result.line = ctx.start.getLine();
+      result.col = ctx.start.getCharPositionInLine();
+      if (ctx.expression() != null) {
+        var error = "Cannot return an expression from a void function.";
+        throw new RuntimeException(Helper.getErrorPrefix(result.line, result.col) + error);
+      }
+      return result;
+    }
+
+    var expression = (Expression) visit(ctx.expression());
 
     // Check if this expression is a tail recursion
-    if (expression instanceof FunctionCall) {
-      var funCall = (FunctionCall) expression;
-      if (funCall.name.equals(this.currentFunctionDefinitionName)) {
+    if (expression instanceof FunctionCall funCall) {
+      if (funCall.name.equals(currentFunctionDefinitionName)) {
         // Flag this function call
         funCall.isTailRecursive = true;
       }
     }
 
-    result.type = expression.type;
+    var result = new ReturnStatement(expression);
     result.line = ctx.start.getLine();
+    result.type = expression.type;
     result.col = ctx.start.getCharPositionInLine();
     return result;
   }
 
   @Override
   public Node visitField_assignment(KlangParser.Field_assignmentContext ctx) {
-    String varName = ctx.IDENT(0).getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    String[] path = new String[ctx.IDENT().size() - 1];
+    var varName = ctx.IDENT(0).getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
+    var path = createStructPath(ctx.IDENT());
 
-    for (int i = 1; i < ctx.IDENT().size(); i++) {
-      path[i - 1] = ctx.IDENT(i).getText();
-    }
+    var variableOrParameter = getVariableOrParameter(varName, line, col);
+    ensureReferencesStruct(variableOrParameter, line, col);
+    var fieldType = drillType(variableOrParameter, path, line, col);
 
-    // Get the referenced variable, make sure it is defined
-    var variableDef = this.vars.get(varName);
-    if (variableDef == null) {
-      String error = "Variable with name " + varName + " not defined.";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
-
-    // Make sure it references a struct
-    if (variableDef.type.isPrimitiveType()) {
-      String error = "Variable must reference a struct but references " + variableDef.type.getName() + ".";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
-
-    // Get the type of the result of this expression
-    String structName = variableDef.type.getName();
-    Type fieldType;
-    try {
-      fieldType = Helper.drillType(this.structs, structName, path, 0);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
-    }
-
-    // Get the expression and make sure the type combines properly
-    Expression expression = (Expression) this.visit(ctx.expression());
+    // Visit the expression and make sure the type combines properly
+    var expression = (Expression) visit(ctx.expression());
     try {
       fieldType.combine(expression.type);
     } catch (Exception e) {
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
     }
 
-    Node result = new FieldAssignment(varName, structName, path, expression);
+    var result = new FieldAssignment(varName, variableOrParameter.type.getName(), path, expression);
     result.col = col;
     result.line = line;
     return result;
   }
 
   @Override
-  public Node visitStructFieldAccessExpression(KlangParser.StructFieldAccessExpressionContext ctx) {
-    String varName = ctx.IDENT(0).getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    String[] path = new String[ctx.IDENT().size() - 1];
+  public Node visitMemberAccessExpression(KlangParser.MemberAccessExpressionContext ctx) {
+    var baseName = ctx.IDENT(0).getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
+    var path = createStructPath(ctx.IDENT());
 
-    for (int i = 1; i < ctx.IDENT().size(); i++) {
-      path[i - 1] = ctx.IDENT(i).getText();
+    // Determine if the base name points to an enum or a variable
+    var enumDef = enumDefs.get(baseName);
+    if (enumDef != null) {
+      if (path.length != 1) {
+        var error = "Illegal access to enum " + enumDef.name + ".";
+        throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+      }
+
+      var enumValueName = path[0];
+      var enumValue = Arrays.stream(enumDef.enums)
+              .filter(e -> e.value.equals(enumValueName))
+              .findFirst()
+              .orElseThrow(() -> {
+                var error = "Unknown enum value " + enumValueName + " of enum " +  enumDef.name + ".";
+                throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+              });
+
+      var enumAccessExpression = new EnumAccessExpression(baseName, enumValueName, enumValue);
+      enumAccessExpression.type = enumDef.type;
+      enumAccessExpression.line = line;
+      enumAccessExpression.col = col;
+
+      return enumAccessExpression;
     }
 
-    // Get the referenced variable, make sure it is defined
-    var variableDef = this.vars.get(varName);
-    if (variableDef == null) {
-      String error = "Variable with name " + varName + " not defined.";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
+    var variableOrParameter = getVariableOrParameter(baseName, line, col);
+    ensureReferencesStruct(variableOrParameter, line, col);
+    var resultType = drillType(variableOrParameter, path, line, col);
 
-    // Make sure it references a struct
-    if (variableDef.type.isPrimitiveType()) {
-      String error = "Variable must reference a struct but references " + variableDef.type.getName() + ".";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
+    var memberAccessExpression = new MemberAccessExpression(baseName, variableOrParameter.type.getName(), path);
+    memberAccessExpression.type = resultType;
+    memberAccessExpression.line = line;
+    memberAccessExpression.col = col;
 
-    // Get the type of the result of this expression
-    String structName = variableDef.type.getName();
-    Type resultType;
-    try {
-      resultType = Helper.drillType(this.structs, structName, path, 0);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
-    }
-
-    Node result = new StructFieldAccessExpression(varName, structName, path);
-    result.type = resultType;
-    result.line = line;
-    result.col = col;
-    return result;
+    return memberAccessExpression;
   }
 
   @Override
@@ -660,24 +680,20 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitVariable(KlangParser.VariableContext ctx) {
-    String name = ctx.IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var variableName = ctx.IDENT().getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    VariableDeclaration var = this.vars.get(name);
-    if (var == null) {
-      String error = "Variable with name \"" + name + "\" not defined.";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
+    var variableOrParameter = getVariableOrParameter(variableName, line, col);
 
     // Make sure the variable has been initialized before it can be used
-    if (!var.initialized) {
-      String error = "Variable with name \"" + name + "\" has not been initialized.";
+    if (!variableOrParameter.initialized) {
+      var error = "Variable with name \"" + variableName + "\" has not been initialized.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    Variable result = new Variable(ctx.IDENT().getText());
-    result.type = var.type;
+    var result = new Variable(ctx.IDENT().getText());
+    result.type = variableOrParameter.type;
     result.line = line;
     result.col = col;
     return result;
@@ -708,7 +724,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitBoolAtom(KlangParser.BoolAtomContext ctx) {
-    Node n = new BooleanExpression(ctx.getText().equals("true") ? true : false);
+    Node n = new BooleanExpression(ctx.getText().equals("true"));
     n.type = Type.getBooleanType();
     n.line = ctx.start.getLine();
     n.col = ctx.start.getCharPositionInLine();
@@ -725,70 +741,146 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
   }
 
   @Override
-  public Node visitFunctionDef(KlangParser.FunctionDefContext ctx) {
-    String name = ctx.funcName.getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    Type returnType = Type.getByName(ctx.returnType.type().getText());
-    this.currentDeclaredReturnType = returnType;
-    this.currentFunctionDefinitionName = name;
+  public Node visitStructDef(KlangParser.StructDefContext ctx) {
+    var structName = ctx.structName.getText();
+    var structFieldCount = ctx.structField().size();
+    var structFields = new StructField[structFieldCount];
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    if (!returnType.isPrimitiveType() && this.structs.get(returnType.getName()) == null) {
-      String error = "Type " + returnType.getName() + " not defined.";
+    for (int i = 0; i < structFieldCount; i++) {
+      structFields[i] = (StructField) visit(ctx.structField(i));
+    }
+
+    var structDef = new StructDefinition(structName, structFields);
+    structDef.type = Type.getByName(structName);
+    structDef.line = line;
+    structDef.col = col;
+
+    return structDef;
+  }
+
+  @Override
+  public Node visitStructField(KlangParser.StructFieldContext ctx) {
+    var structFieldName = ctx.IDENT().getText();
+    var structFieldType = Type.getByName(ctx.type_annotation().type().getText());
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
+
+    if (structFieldType.equals(Type.getVoidType())) {
+      var error = "Type void can not be used as a struct field type.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    // Create a new set for the variables of the current function
-    // this will be filled in the variable declaration visitor aswell
-    this.vars = new HashMap<>();
+    if (!structFieldType.isPrimitiveType() && !structDefs.containsKey(structFieldType.getName()) && !enumDefs.containsKey(structFieldType.getName())) {
+      var error = "Type " + structFieldType.getName() + " not defined.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
 
-    // Process the paremter list by visiting every paremter in it
-    int paramCount = ctx.params.parameter().size();
-    Parameter[] params = new Parameter[paramCount];
+    if (structDefs.containsKey(structFieldName)) {
+      var error = "Struct field name " + structFieldName + " shadows a struct of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (enumDefs.containsKey(structFieldName)) {
+      var error = "Struct field name " + structFieldName + " shadows an enum of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    var structField = new StructField(structFieldName);
+    structField.type = structFieldType;
+    structField.line = line;
+    structField.col = col;
+
+    return structField;
+  }
+
+  @Override
+  public Node visitFunctionDef(KlangParser.FunctionDefContext ctx) {
+    var name = ctx.funcName.getText();
+    var returnType = Type.getByName(ctx.returnType.type().getText());
+    currentDeclaredReturnType = returnType;
+    currentFunctionDefinitionName = name;
+
+    var typeNotDefined = !returnType.isPrimitiveType() && !structDefs.containsKey(returnType.getName()) && !enumDefs.containsKey(returnType.getName());
+    if (!returnType.equals(Type.getVoidType()) && typeNotDefined) {
+      var line = ctx.returnType.start.getLine();
+      var col = ctx.returnType.start.getCharPositionInLine();
+      var error = "Type " + returnType.getName() + " not defined.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    // Create a new set for the variables and parameters of the current function
+    // this will be filled in the variable declaration visitor as well
+    vars = new HashMap<>();
+    params = new HashMap<>();
+
+
+    var paramCount = ctx.params.parameter().size();
+    var functionParameters = new Parameter[paramCount]; // the list of parameters that get passed to FunctionDefinition
     for (int i = 0; i < paramCount; i++) {
-      // Add the parameter to the list of parameters
-      Parameter param = (Parameter) this.visit(ctx.params.parameter(i));
-      params[i] = param;
+      functionParameters[i] = (Parameter) visit(ctx.params.parameter(i));
 
-      // add the param as a variable
-      VariableDeclaration var = new VariableDeclaration(param.name);
-      var.initialized = true; // parameters can always be considered initialized
-      var.type = param.type;
-      this.vars.put(param.name, var);
+      // add the param as a variable to the global parameter map so that
+      // child nodes can access them.
+      var param = new VariableDeclaration(functionParameters[i].name);
+      param.initialized = true; // parameters can always be considered initialized
+      param.type = functionParameters[i].type;
+      params.put(param.name, param);
     }
 
     // Visit the block, make sure that a return value is guaranteed
-    Node block = this.visit(ctx.braced_block());
-    if (block.type == null) {
-      String error = "Function " + name + " has to return something of type " + returnType.getName() + ".";
+    var block = visit(ctx.braced_block());
+    if (block.type == null && !returnType.equals(Type.getVoidType())) {
+      var line = ctx.braced_block().start.getLine();
+      var col = ctx.braced_block().start.getCharPositionInLine();
+      var error = "Function " + name + " has to return something of type " + returnType.getName() + ".";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    FunctionDefinition result = new FunctionDefinition(name, params, (Block) block);
-    result.type = returnType;
+    var functionDef = new FunctionDefinition(name, functionParameters, vars.values().toArray(new VariableDeclaration[0]), (Block) block);
+    functionDef.type = returnType;
+    functionDef.line = ctx.start.getLine();
+    functionDef.col = ctx.start.getCharPositionInLine();
 
-    result.line = ctx.start.getLine();
-    result.col = ctx.start.getCharPositionInLine();
-    return result;
+    return functionDef;
   }
 
   @Override
   public Node visitParameter(KlangParser.ParameterContext ctx) {
-    String name = ctx.IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    Type type = Type.getByName(ctx.type_annotation().type().getText());
+    var parameterName = ctx.IDENT().getText();
+    var parameterType = Type.getByName(ctx.type_annotation().type().getText());
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    if (!type.isPrimitiveType() && this.structs.get(type.getName()) == null) {
-      String error = "Type " + type.getName() + " not defined.";
+    if (parameterType.equals(Type.getVoidType())) {
+      var error = "Type " + parameterType.getName() + " cannot be used to declare a parameter.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    Parameter result = new Parameter(name);
-    result.type = type;
-    result.line = line;
-    result.col = col;
-    return result;
+    if (structDefs.containsKey(parameterName)) {
+      var error = "Parameter name " + parameterName + " duplicates a struct of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (enumDefs.containsKey(parameterName)) {
+      var error = "Parameter name " + parameterName + " duplicates an enum of the same name.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    if (!parameterType.isPrimitiveType() && !structDefs.containsKey(parameterType.getName()) && !enumDefs.containsKey(parameterType.getName())) {
+      var typeLine = ctx.type_annotation().start.getLine();
+      var typeCol = ctx.type_annotation().start.getCharPositionInLine();
+      var error = "Type " + parameterType.getName() + " not defined.";
+      throw new RuntimeException(Helper.getErrorPrefix(typeLine, typeCol) + error);
+    }
+
+    var parameter = new Parameter(parameterName);
+    parameter.type = parameterType;
+    parameter.line = ctx.start.getLine();
+    parameter.col = ctx.start.getCharPositionInLine();
+
+    return parameter;
   }
 
   @Override
@@ -797,15 +889,15 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     int line = ctx.start.getLine();
     int col = ctx.start.getCharPositionInLine();
 
-    FunctionInformation func = this.funcs.get(name);
-    if (func == null) {
+    var functionDef = this.functionDefs.get(name);
+    if (functionDef == null) {
       String error = "Function with name \"" + name + "\" not defined.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
     // Make sure the number of arguments matches the number of parameters
     int argCount = ctx.functionCall().arguments().expression().size();
-    int paramCount = func.parameters.size();
+    int paramCount = functionDef.parameters.length;
     if (argCount != paramCount) {
       String error = "Function \"" + name + "\" expects " + paramCount + " parameters, but got " + argCount + ".";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
@@ -815,14 +907,14 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     Expression[] args = new Expression[argCount];
     for (int i = 0; i < argCount; i++) {
       Expression expression = (Expression) this.visit(ctx.functionCall().arguments().expression(i));
-      if (!expression.type.equals(func.signature[i])) {
-        throw new RuntimeException(Helper.getErrorPrefix(line, col) + "argument " + i + " Expected " + func.signature[i].getName() + " but got: " + expression.type.getName());
+      if (!expression.type.equals(functionDef.parameters[i].type)) {
+        throw new RuntimeException(Helper.getErrorPrefix(line, col) + "argument " + i + " Expected " + functionDef.parameters[i].type.getName() + " but got: " + expression.type.getName());
       }
       args[i] = expression;
     }
 
     FunctionCall result = new FunctionCall(name, args);
-    result.type = func.returnType;
+    result.type = functionDef.type;
     result.line = line;
     result.col = col;
     return result;
@@ -835,7 +927,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     int col = ctx.start.getCharPositionInLine();
     
     // Get the corresponding struct definition
-    var struct = this.structs.get(name);
+    var struct = this.structDefs.get(name);
     if (struct == null) {
       String error = "Struct with name \"" + name + "\" not defined.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
@@ -870,19 +962,52 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitDestroy_statement(KlangParser.Destroy_statementContext ctx) {
-    String name = ctx.IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-    
-    VariableDeclaration var = this.vars.get(name);
-    if (var == null) {
-      String error = "Variable with name \"" + name + "\" not defined.";
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-    }
+    var varName = ctx.IDENT().getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    Node result = new DestructorCall(name);
+    var variableOrParameter = getVariableOrParameter(varName, line, col);
+    ensureReferencesStruct(variableOrParameter, line, col);
+
+    var result = new DestructorCall(varName);
     result.line = line;
     result.col = col;
     return result;
   }
-}
+
+  private VariableDeclaration getVariableOrParameter(String name, int line, int col) {
+    var variable = vars.get(name);
+    var parameter = params.get(name);
+    if (variable == null && parameter == null) {
+      var error = "Variable or parameter with name \"" + name + "\" not defined.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+
+    return variable != null ? variable : parameter;
+  }
+
+  private void ensureReferencesStruct(VariableDeclaration variableOrParameter, int line, int col) {
+    if (variableOrParameter.type.isPrimitiveType() || enumDefs.containsKey(variableOrParameter.type.getName())) {
+      var error = "Variable or parameter must reference a struct but references " + variableOrParameter.type.getName() + ".";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
+  }
+
+  private Type drillType(VariableDeclaration variableOrParameter, String[] path, int line, int col) {
+    try {
+      var structName = variableOrParameter.type.getName();
+      return Helper.drillType(structDefs, structName, path, 0);
+    } catch (Exception e) {
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
+    }
+  }
+
+  private String[] createStructPath(List<TerminalNode> identifiers) {
+    // Create a list of member names. This excludes the first entry as it is the base name.
+    var path = new String[identifiers.size() - 1];
+    for (int i = 1; i < identifiers.size(); i++) {
+      path[i - 1] = identifiers.get(i).getText();
+    }
+    return path;
+  }
+}

src/main/java/de/hsrm/compiler/Klang/GetDefinitions.java

@@ -0,0 +1,220 @@
+package de.hsrm.compiler.Klang;
+
+import de.hsrm.compiler.Klang.helper.Helper;
+import de.hsrm.compiler.Klang.nodes.*;
+import de.hsrm.compiler.Klang.types.NamedType;
+import de.hsrm.compiler.Klang.types.Type;
+
+import java.util.*;
+
+public class GetDefinitions extends KlangBaseVisitor<Node> {
+    private final Map<String, FunctionDefinition> functionDefs;
+    private final Map<String, StructDefinition> structDefs;
+    private final Map<String, EnumDefinition> enumDefs;
+
+    private Set<String> functionNames;
+    private Set<String> structNames;
+    private Set<String> enumNames;
+
+    public GetDefinitions(
+            Map<String, FunctionDefinition> functionDefs,
+            Map<String, StructDefinition> structDefs,
+            Map<String, EnumDefinition> enumDefs
+    ) {
+        this.functionDefs = functionDefs;
+        this.structDefs = structDefs;
+        this.enumDefs = enumDefs;
+    }
+
+    private Set<String> collectFunctionNames(KlangParser.ProgramContext ctx) {
+        var result = new HashSet<String>();
+        for (int i = 0; i < ctx.functionDef().size(); i++) {
+            var currentFunctionDef = ctx.functionDef(i);
+            var funcName = currentFunctionDef.funcName.getText();
+            if (result.contains(funcName)) {
+                var line = currentFunctionDef.funcName.getLine();
+                var col = currentFunctionDef.funcName.getCharPositionInLine();
+                var error = "Function " + funcName + " defined multiple times.";
+                throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+            }
+            result.add(funcName);
+        }
+        return result;
+    }
+
+    private Set<String> collectStructNames(KlangParser.ProgramContext ctx) {
+        var result = new HashSet<String>();
+        for (int i = 0; i < ctx.structDef().size(); i++) {
+            var currentStructDef = ctx.structDef(i);
+            var structName = currentStructDef.structName.getText();
+            if (result.contains(structName)) {
+                var line = currentStructDef.structName.getLine();
+                var col = currentStructDef.structName.getCharPositionInLine();
+                var error = "Struct " + structName + " defined multiple times.";
+                throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+            }
+            result.add(structName);
+        }
+        return result;
+    }
+
+    private Set<String> collectEnumNames(KlangParser.ProgramContext ctx) {
+        var result = new HashSet<String>();
+        for (int i = 0; i < ctx.enumDef().size(); i++) {
+            var currentEnumDef = ctx.enumDef(i);
+            var enumName = currentEnumDef.enumName.getText();
+            if (result.contains(enumName)) {
+                var line = currentEnumDef.enumName.getLine();
+                var col = currentEnumDef.enumName.getCharPositionInLine();
+                var error = "Enum " + enumName + " defined multiple times.";
+                throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+            }
+            result.add(enumName);
+        }
+        return result;
+    }
+
+    @Override
+    public Node visitProgram(KlangParser.ProgramContext ctx) {
+        functionNames = collectFunctionNames(ctx);
+        structNames = collectStructNames(ctx);
+        enumNames = collectEnumNames(ctx);
+
+        for (int i = 0; i < ctx.functionDef().size(); i++) {
+            visit(ctx.functionDef(i));
+        }
+
+        for (int i = 0; i < ctx.structDef().size(); i++) {
+            visit(ctx.structDef(i));
+        }
+
+        for (int i = 0; i < ctx.enumDef().size(); i++) {
+            visit(ctx.enumDef(i));
+        }
+
+        return null;
+    }
+
+    @Override
+    public Node visitEnumDef(KlangParser.EnumDefContext ctx) {
+        // Check that there isn't a function or struct with the same name
+        var enumName = ctx.enumName.getText();
+        if (functionNames.contains(enumName) || structNames.contains(enumName)) {
+            var line = ctx.start.getLine();
+            var col = ctx.start.getCharPositionInLine();
+            var error = "Duplicate use of name " + enumName + ".";
+            throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+        }
+
+        // IDENT() includes the enumName as the first entry, which we skip
+        var enumValues = new LinkedHashMap<String, EnumValue>();
+        for (int i = 1; i < ctx.IDENT().size(); i++) {
+            var currentEnumField = ctx.IDENT(i);
+            var currentEnumFieldName = currentEnumField.getText();
+            var line = currentEnumField.getSymbol().getLine();
+            var col = currentEnumField.getSymbol().getCharPositionInLine();
+
+            if (enumValues.containsKey(currentEnumFieldName)) {
+                var error = " Duplicate enum value " + currentEnumFieldName + " in enum " + enumName + ".";
+                throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+            }
+
+            var enumValue = new EnumValue(currentEnumFieldName, i - 1);
+            enumValue.line = line;
+            enumValue.col = col;
+
+            enumValues.put(currentEnumFieldName, enumValue);
+        }
+
+        var enumDef = new EnumDefinition(enumName, enumValues.values().toArray(new EnumValue[0]));
+        enumDef.line = ctx.start.getLine();
+        enumDef.col = ctx.start.getCharPositionInLine();
+        enumDef.type = new NamedType(enumName);
+        enumDefs.put(enumName, enumDef);
+
+        return null;
+    }
+
+    @Override
+    public Node visitStructDef(KlangParser.StructDefContext ctx) {
+        var structName = ctx.structName.getText();
+        var structFieldCount = ctx.structField().size();
+        var structFields = new LinkedHashMap<String, StructField>();
+        var line = ctx.start.getLine();
+        var col = ctx.start.getCharPositionInLine();
+
+        // Check that there isn't a function or enum with the same name
+        if (functionNames.contains(structName) || enumNames.contains(structName)) {
+            var error = "Duplicate use of name " + structName + ".";
+            throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+        }
+
+        for (int i = 0; i < structFieldCount; i++) {
+            var currentStructField = ctx.structField(i);
+            var structFieldName = currentStructField.IDENT().getText();
+            var structFieldLine = currentStructField.start.getLine();
+            var structFieldCol = currentStructField.start.getCharPositionInLine();
+
+            if (structFields.containsKey(structFieldName)) {
+                var error = "Duplicate struct field " + structFieldName + " in struct " + structName + ".";
+                throw new RuntimeException(Helper.getErrorPrefix(structFieldLine, structFieldCol) + error);
+            }
+
+            var structField = new StructField(structFieldName);
+            structField.type = Type.getByName(currentStructField.type_annotation().type().getText());
+            structField.line = structFieldLine;
+            structField.col = structFieldCol;
+
+            structFields.put(structFieldName, structField);
+        }
+
+        var structDef = new StructDefinition(structName, structFields.values().toArray(new StructField[0]));
+        structDef.line = line;
+        structDef.col = col;
+        structDef.type = new NamedType(structName);
+        structDefs.put(structName, structDef);
+
+        return null;
+    }
+
+    @Override
+    public Node visitFunctionDef(KlangParser.FunctionDefContext ctx) {
+        var funcName = ctx.funcName.getText();
+        var paramCount = ctx.params.parameter().size();
+        var parameters = new LinkedHashMap<String, Parameter>();
+        var line = ctx.start.getLine();
+        var col = ctx.start.getCharPositionInLine();
+
+        // Check that there isn't a struct or enum with the same name
+        if (structNames.contains(funcName) || enumNames.contains(funcName)) {
+            var error = "Duplicate use of name " + funcName + ".";
+            throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+        }
+
+        for (int i = 0; i < paramCount; i++) {
+            var currentParam = ctx.params.parameter(i);
+            var paramName = currentParam.IDENT().getText();
+            var paramLine = currentParam.start.getLine();
+            var paramCol = currentParam.start.getCharPositionInLine();
+
+            if (parameters.containsKey(paramName)) {
+                var error = "Duplicate parameter name " + paramName + " in function " + funcName + ".";
+                throw new RuntimeException(Helper.getErrorPrefix(paramLine, paramCol) + error);
+            }
+
+            var parameter = new Parameter(paramName);
+            parameter.type = Type.getByName(currentParam.type_annotation().type().getText());
+            parameter.line = paramLine;
+            parameter.col = paramCol;
+
+            parameters.put(paramName, parameter);
+        }
+
+        var functionDef = new FunctionDefinition(funcName, parameters.values().toArray(new Parameter[0]), null, null);
+        functionDef.type = Type.getByName(ctx.returnType.type().getText());
+        functionDef.line = line;
+        functionDef.col = col;
+        functionDefs.put(funcName, functionDef);
+        return null;
+    }
+}

src/main/java/de/hsrm/compiler/Klang/GetFunctions.java

@@ -1,54 +0,0 @@
-package de.hsrm.compiler.Klang;
-
-import java.util.Map;
-import java.util.TreeMap;
-
-import de.hsrm.compiler.Klang.types.*;
-import de.hsrm.compiler.Klang.helper.*;
-
-public class GetFunctions extends KlangBaseVisitor<Void> {
-
-  private Map<String, FunctionInformation> funcs;
-
-  public GetFunctions(Map<String, FunctionInformation> funcs) {
-    this.funcs = funcs;
-  }
-
-  @Override
-  public Void visitProgram(KlangParser.ProgramContext ctx) {
-    for (int i = 0; i < ctx.functionDef().size(); i++) {
-      this.visit(ctx.functionDef(i));
-    }
-    return null;
-  }
-
-  @Override
-  public Void visitFunctionDef(KlangParser.FunctionDefContext ctx) {
-    String name = ctx.funcName.getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
-
-    if (this.funcs.containsKey(name)) {
-      String error = "Function " + name + " defined multiple times.";
-      throw new Error(Helper.getErrorPrefix(line, col) + error);
-    }
-    
-    Type returnType = Type.getByName(ctx.returnType.type().getText());
-
-    TreeMap<String, Type> parameters = new TreeMap<String, Type>();
-
-    // Process the paremter list by visiting every paremter in it
-    int paramCount = ctx.params.parameter().size();
-    Type[] signature = new Type[paramCount];
-    for (int i = 0; i < paramCount; i++) {
-      Type paramType = Type.getByName(ctx.params.parameter(i).type_annotation().type().getText());
-      String paramName = ctx.params.parameter(i).IDENT().getText();
-      parameters.put(paramName, paramType);
-      signature[i] = paramType;
-    }
-
-    FunctionInformation information = new FunctionInformation(name, returnType, parameters, signature);
-    this.funcs.put(name, information);
-    return null;
-  }
-}

src/main/java/de/hsrm/compiler/Klang/GetStructNames.java

@@ -1,37 +0,0 @@
-package de.hsrm.compiler.Klang;
-
-import java.util.Set;
-
-import de.hsrm.compiler.Klang.helper.Helper;
-
-public class GetStructNames extends KlangBaseVisitor<Void> {
-    private Set<String> structNames;
-
-    public GetStructNames(Set<String> structNames) {
-        this.structNames = structNames;
-    }
-
-    @Override
-    public Void visitProgram(KlangParser.ProgramContext ctx) {
-        for (int i = 0; i < ctx.structDef().size(); i++) {
-            this.visit(ctx.structDef(i));
-        }
-
-        return null;
-    }
-
-    @Override
-    public Void visitStructDef(KlangParser.StructDefContext ctx) {
-        String name = ctx.structName.getText();
-        int line = ctx.start.getLine();
-        int col = ctx.start.getCharPositionInLine();
-
-        if (this.structNames.contains(name)) {
-            String error = "Struct " + name + " defined multiple times.";
-            throw new Error(Helper.getErrorPrefix(line, col) + error);
-        }
-
-        this.structNames.add(name);
-        return null;
-    }
-}

src/main/java/de/hsrm/compiler/Klang/GetStructs.java

@@ -1,70 +0,0 @@
-package de.hsrm.compiler.Klang;
-
-import java.util.Map;
-import java.util.Set;
-
-import de.hsrm.compiler.Klang.helper.Helper;
-import de.hsrm.compiler.Klang.nodes.Node;
-import de.hsrm.compiler.Klang.nodes.StructDefinition;
-import de.hsrm.compiler.Klang.nodes.StructField;
-import de.hsrm.compiler.Klang.types.StructType;
-import de.hsrm.compiler.Klang.types.Type;
-
-public class GetStructs extends KlangBaseVisitor<Node> {
-
-    private Set<String> structNames;
-    private Map<String, StructDefinition> structs;
-
-    public GetStructs(Set<String> structNames, Map<String, StructDefinition> structs) {
-        this.structs = structs;
-        this.structNames = structNames;
-    }
-
-    @Override
-    public Node visitProgram(KlangParser.ProgramContext ctx) {
-        for (int i = 0; i < ctx.structDef().size(); i++) {
-            this.visit(ctx.structDef(i));
-        }
-
-        return null;
-    }
-
-    @Override
-    public Node visitStructDef(KlangParser.StructDefContext ctx) {
-        String name = ctx.structName.getText();
-        int line = ctx.start.getLine();
-        int col = ctx.start.getCharPositionInLine();
-        StructField[] fields = new StructField[ctx.structField().size()];
-    
-        for (int i = 0; i < ctx.structField().size(); i++) {
-          StructField field = (StructField) this.visit(ctx.structField(i));
-          fields[i] = field;
-        }
-    
-        StructDefinition result = new StructDefinition(name, fields);
-        result.line = line;
-        result.col = col;
-        result.type = new StructType(name);
-        this.structs.put(name, result);
-        return null;
-    }
-
-    @Override
-    public Node visitStructField(KlangParser.StructFieldContext ctx) {
-      String name = ctx.IDENT().getText();
-      int line = ctx.start.getLine();
-      int col = ctx.start.getCharPositionInLine();
-      Type type = Type.getByName(ctx.type_annotation().type().getText());
-  
-      if (!type.isPrimitiveType() && !this.structNames.contains(type.getName())) {
-        String error = "Type " + type.getName() + " not defined.";
-        throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
-      }
-  
-      Node result = new StructField(name);
-      result.type = type;
-      result.line = line;
-      result.col = col;
-      return result;
-    }
-}

src/main/java/de/hsrm/compiler/Klang/Klang.java

@@ -1,19 +1,24 @@
 package de.hsrm.compiler.Klang;
 
-// import ANTLR's runtime libraries
-import org.antlr.v4.runtime.*;
-import org.antlr.v4.runtime.tree.*;
-
-import java.io.*;
-import java.util.Arrays;
-import java.util.List;
-import java.util.HashMap;
-import java.util.HashSet;
-
+import de.hsrm.compiler.Klang.helper.*;
+import de.hsrm.compiler.Klang.nodes.EnumDefinition;
+import de.hsrm.compiler.Klang.nodes.FunctionDefinition;
 import de.hsrm.compiler.Klang.nodes.Node;
 import de.hsrm.compiler.Klang.nodes.StructDefinition;
-import de.hsrm.compiler.Klang.visitors.*;
-import de.hsrm.compiler.Klang.helper.*;
+import de.hsrm.compiler.Klang.types.Type;
+import de.hsrm.compiler.Klang.visitors.EvalVisitor;
+import de.hsrm.compiler.Klang.visitors.GenASM;
+import de.hsrm.compiler.Klang.visitors.PrettyPrintVisitor;
+import org.antlr.v4.runtime.CharStream;
+import org.antlr.v4.runtime.CharStreams;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+
+import java.io.FileWriter;
+import java.io.StringWriter;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
 
 public class Klang {
 
@@ -87,22 +92,15 @@ public class Klang {
 
     // Context Analysis and DAST generation
     Node root;
-    HashMap<String, StructDefinition> structs;
+    var functionDefs = new HashMap<String, FunctionDefinition>();
+    var structDefs = new HashMap<String, StructDefinition>();
+    var enumDefs = new HashMap<String, EnumDefinition>();
     try {
-      // Extract information about all functions
-      var functionDefinitions = new HashMap<String, FunctionInformation>();
-      new GetFunctions(functionDefinitions).visit(tree);
-
-      // Extract names of all structs
-      var structNames = new HashSet<String>();
-      new GetStructNames(structNames).visit(tree);
-
-      // Extract information about all structs
-      structs = new HashMap<String, StructDefinition>();
-      new GetStructs(structNames, structs).visit(tree);
+      // Extract information about all definitions
+      new GetDefinitions(functionDefs, structDefs, enumDefs).visit(tree);
 
       // Create the DAST
-      ContextAnalysis ctxAnal = new ContextAnalysis(functionDefinitions, structs);
+      ContextAnalysis ctxAnal = new ContextAnalysis(functionDefs, structDefs, enumDefs);
       root = ctxAnal.visit(tree);
     } catch (Exception e) {
       System.err.println(e.getMessage());
@@ -122,18 +120,19 @@ public class Klang {
     if (evaluate) {
       // Evaluate the sourcecode and print the result
       System.out.println("\nEvaluating the source code:");
-      EvalVisitor evalVisitor = new EvalVisitor(structs);
+      EvalVisitor evalVisitor = new EvalVisitor(structDefs);
       Value result = root.welcome(evalVisitor);
-      generateOutput(out, "Result was: " + result.asObject().toString());
+      if (result.type.equals(Type.getVoidType())) {
+        generateOutput(out, "Result was void");
+      } else {
+        generateOutput(out, "Result was: " + result.asObject().toString());
+      }
       return;
     }
 
     // Generate assembler code
-    // System.out.println("\nPrinting the assembler code");
-    StringWriter wAsm = new StringWriter();
-    GenASM.ExWriter exAsm = new GenASM.ExWriter(wAsm);
-    GenASM genasm = new GenASM(exAsm, mainName, structs);
+    GenASM genasm = new GenASM(mainName, structDefs);
     root.welcome(genasm);
-    generateOutput(out, wAsm.toString());
+    generateOutput(out, genasm.toAsm());
   }
 }

src/main/java/de/hsrm/compiler/Klang/asm/ASM.java

@@ -0,0 +1,222 @@
+package de.hsrm.compiler.Klang.asm;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import de.hsrm.compiler.Klang.asm.mnemonics.*;
+
+public class ASM {
+  private List<Mnemonic> mnemonics;
+
+  public ASM() {
+    this.mnemonics = new ArrayList<Mnemonic>();
+  }
+
+  public void push(String dataType, int immediate) {
+    mnemonics.add(new Push(dataType, immediate));
+  }
+
+  public void push(String dataType, String operand) {
+    mnemonics.add(new Push(dataType, operand));
+  }
+
+  public void pop(String dataType, String operand) {
+    mnemonics.add(new Pop(dataType, operand));
+  }
+
+  public void mov(String dataType, String src, String dst) {
+    mnemonics.add(new Mov(dataType, src, dst));
+  }
+
+  public void mov(String dataType, String label, String src, String dst) {
+    mnemonics.add(new Mov(dataType, label, src, dst));
+  }
+
+  public void mov(String dataType, int offset, String src, String dst) {
+    mnemonics.add(new Mov(dataType, offset, src, dst));
+  }
+
+  public void mov(String dataType, String src, int offset, String dst) {
+    mnemonics.add(new Mov(dataType, src, offset, dst));
+  }
+
+  public void mov(String dataType, int immediate, String dst) {
+    mnemonics.add(new Mov(dataType, immediate, dst));
+  }
+
+  public void ucomi(String dataType, String src, String dst) {
+    mnemonics.add(new Ucomi(dataType, src, dst));
+  }
+
+  public void cmp(String dataType, String src, String dst) {
+    mnemonics.add(new Cmp(dataType, src, dst));
+  }
+
+  public void cmp(String dataType, int immediate, String dst) {
+    mnemonics.add(new Cmp(dataType, immediate, dst));
+  }
+
+  public void je(int label) {
+    mnemonics.add(new Je(label));
+  }
+
+  public void je(String labelPrefix, int label) {
+    mnemonics.add(new Je(labelPrefix, label));
+  }
+
+  public void jmp(int label) {
+    mnemonics.add(new Jmp(label));
+  }
+
+  public void jmp(String labelPrefix, int label) {
+    mnemonics.add(new Jmp(labelPrefix, label));
+  }
+
+  public void jne(int label) {
+    mnemonics.add(new Jne(label));
+  }
+
+  public void jne(String labelPrefix, int label) {
+    mnemonics.add(new Jne(labelPrefix, label));
+  }
+
+  public void jg(int label) {
+    mnemonics.add(new Jg(label));
+  }
+
+  public void jg(String labelPrefix, int label) {
+    mnemonics.add(new Jg(labelPrefix, label));
+  }
+
+  public void jge(int label) {
+    mnemonics.add(new Jge(label));
+  }
+
+  public void jge(String labelPrefix, int label) {
+    mnemonics.add(new Jge(labelPrefix, label));
+  }
+
+  public void jl(int label) {
+    mnemonics.add(new Jl(label));
+  }
+
+  public void jl(String labelPrefix, int label) {
+    mnemonics.add(new Jl(labelPrefix, label));
+  }
+
+  public void jle(int label) {
+    mnemonics.add(new Jle(label));
+  }
+
+  public void jle(String labelPrefix, int label) {
+    mnemonics.add(new Jle(labelPrefix, label));
+  }
+
+  public void jz(int label) {
+    mnemonics.add(new Jz(label));
+  }
+
+  public void jz(String labelPrefix, int label) {
+    mnemonics.add(new Jz(labelPrefix, label));
+  }
+
+  public void jnz(int label) {
+    mnemonics.add(new Jnz(label));
+  }
+
+  public void jnz(String labelPrefix, int label) {
+    mnemonics.add(new Jnz(labelPrefix, label));
+  }
+
+  public void label(int label) {
+    mnemonics.add(new Label(label));
+  }
+
+  public void label(String labelPrefix, int label) {
+    mnemonics.add(new Label(labelPrefix, label));
+  }
+
+  public void add(String dataType, String src, String dst) {
+    mnemonics.add(new Add(dataType, src, dst));
+  }
+
+  public void add(String dataType, String src, int dstOffset, String dst) {
+    mnemonics.add(new Add(dataType, src, dstOffset, dst));
+  }
+
+  public void add(String dataType, int immediate, String dst) {
+    mnemonics.add(new Add(dataType, immediate, dst));
+  }
+  
+  public void sub(String dataType, String src, String dst) {
+    mnemonics.add(new Sub(dataType, src, dst));
+  }
+  
+  public void mul(String dataType, String src, String dst) {
+    mnemonics.add(new Mul(dataType, src, dst));
+  }
+  
+  public void div(String dataType, String src, String dst) {
+    mnemonics.add(new Div(dataType, src, dst));
+  }
+
+  public void idiv(String dataType, String operand) {
+    mnemonics.add(new Idiv(dataType, operand));
+  }
+  
+  public void imul(String dataType, String src, String dst) {
+    mnemonics.add(new Imul(dataType, src, dst));
+  }
+
+  public void cqto() {
+    mnemonics.add(new Cqto());
+  }
+
+  public void leave() {
+    mnemonics.add(new Leave());
+  }
+
+  public void ret() {
+    mnemonics.add(new Ret());
+  }
+
+  public void xor(String dataType, String src, String dst) {
+    mnemonics.add(new Xor(dataType, src, dst));
+  }
+
+  public void neg(String operand) {
+    mnemonics.add(new Neg(operand));
+  }
+
+  public void functionHead(String functionName) {
+    mnemonics.add(new FunctionHead(functionName));
+  }
+
+  public void call(String operand) {
+    mnemonics.add(new Call(operand));
+  }
+  
+  public void text(String text) {
+    mnemonics.add(new Text(text));
+  }
+
+  public void newline() {
+    mnemonics.add(new Newline());
+  }
+
+  public void cvtsi2sd(String src, String dst) {
+    mnemonics.add(new Cvtsi2sd(src, dst));
+  }
+
+  public String toAsm() {
+    StringBuilder sb = new StringBuilder();
+    mnemonics.stream().forEach(x -> {
+      for (int i = 0; i < x.indentation; i++) {
+        sb.append("\t");
+      }
+      sb.append(x.toAsm());
+      sb.append("\n");
+    });
+    return sb.toString();
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Add.java

@@ -0,0 +1,29 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Add extends TwoOperandMnemonic {
+  public String dataType;
+  
+  public Add(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  public Add(String dataType, String src, int dstOffset, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dstOffset + "(" + dst + ")";
+  }
+
+  public Add(String dataType, int immediate, String dst) {
+    this.dataType = dataType;
+    this.src = "$" + immediate;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "add" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Call.java

@@ -0,0 +1,14 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Call extends OneOperandMnemonic {
+
+  public Call(String operand) {
+    this.operand = operand;
+  }
+
+  @Override
+  public String toAsm() {
+    return "call " + this.operand; 
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Cmp.java

@@ -0,0 +1,22 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Cmp extends TwoOperandMnemonic {
+  public String dataType;
+  
+  public Cmp(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  public Cmp(String dataType, int immediate, String dst) {
+    this.dataType = dataType;
+    this.src = "$" + immediate;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "cmp" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Cqto.java

@@ -0,0 +1,8 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Cqto extends NoOperandMnemonic {
+  @Override
+  public String toAsm() {
+    return "cqto";
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Cvtsi2sd.java

@@ -0,0 +1,15 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Cvtsi2sd extends TwoOperandMnemonic {
+
+  public Cvtsi2sd(String src, String dst) {
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "cvtsi2sd " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Div.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Div extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Div(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "div" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/FunctionHead.java

@@ -0,0 +1,26 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class FunctionHead extends NoOperandMnemonic {
+
+  public String functionName;
+
+  public FunctionHead(String functionName) {
+    this.functionName = functionName;
+    this.indentation = 0;
+  }
+
+  @Override
+  public String toAsm() {
+    StringBuilder sb = new StringBuilder();
+    sb.append(".globl ");
+    sb.append(this.functionName);
+    sb.append("\n");
+    sb.append(".type ");
+    sb.append(this.functionName);
+    sb.append(", @function\n");
+    sb.append(this.functionName);
+    sb.append(":");
+    return sb.toString();
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Idiv.java

@@ -0,0 +1,16 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Idiv extends OneOperandMnemonic{
+  public String dataType;
+
+  public Idiv(String dataType, String operand) {
+    this.dataType = dataType;
+    this.operand = operand;
+  }
+
+  @Override
+  public String toAsm() {
+    return "idiv" + this.dataType + " " + this.operand;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Imul.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Imul extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Imul(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "imul" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Je.java

@@ -0,0 +1,12 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Je extends Jump {
+  
+  public Je(int label) {
+    super("je", label);
+  }
+
+  public Je(String labelPrefix, int label) {
+    super("je", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jg.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jg extends Jump {
+  public Jg(int label) {
+    super("jg", label);
+  }
+
+  public Jg(String labelPrefix, int label) {
+    super("jg", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jge.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jge extends Jump {
+  public Jge(int label) {
+    super("jge", label);
+  }
+
+  public Jge(String labelPrefix, int label) {
+    super("jge", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jl.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jl extends Jump {
+  public Jl(int label) {
+    super("jl", label);
+  }
+
+  public Jl(String labelPrefix, int label) {
+    super("jl", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jle.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jle extends Jump {
+  public Jle(int label) {
+    super("jle", label);
+  }
+
+  public Jle(String labelPrefix, int label) {
+    super("jle", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jmp.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jmp extends Jump {
+  public Jmp(String labelPrefix, int label) {
+    super("jmp", labelPrefix, label);
+  }
+
+  public Jmp(int label) {
+    super("jmp", label);
+  }  
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jne.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jne extends Jump {
+  public Jne(int label) {
+    super("jne", label);
+  }
+
+  public Jne(String labelPrefix, int label) {
+    super("jne", labelPrefix, label);
+  } 
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jnz.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jnz extends Jump {
+  public Jnz(int label) {
+    super("jnz", label);
+  }
+
+  public Jnz(String labelPrefix, int label) {
+    super("jnz", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jump.java

@@ -0,0 +1,21 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public abstract class Jump extends Mnemonic {
+  protected String opcode;
+  public String labelPrefix = "L";
+  public int label;
+  public Jump(String opcode, String labelPrefix, int label) {
+    this.opcode = opcode;
+    this.labelPrefix = labelPrefix;
+    this.label = label;
+  }
+
+  public Jump(String opcode, int label) {
+    this.opcode = opcode;
+    this.label = label;
+  }
+  @Override
+  public String toAsm() {
+    return this.opcode + " ." + this.labelPrefix + this.label;
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Jz.java

@@ -0,0 +1,11 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Jz extends Jump {
+  public Jz(int label) {
+    super("jz", label);
+  }
+
+  public Jz(String labelPrefix, int label) {
+    super("jz", labelPrefix, label);
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Label.java

@@ -0,0 +1,22 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Label extends Mnemonic {
+  public String labelPrefix = "L";
+  public int label;
+
+  public Label(int label) {
+    this.label = label;
+    this.indentation = 0;
+  }
+  
+  public Label(String labelPrefix, int label) {
+    this.labelPrefix = labelPrefix;
+    this.label = label;
+    this.indentation = 0;
+  }
+
+  @Override
+  public String toAsm() {
+    return "." + this.labelPrefix + this.label + ":";
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Leave.java

@@ -0,0 +1,8 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Leave extends NoOperandMnemonic {
+    @Override
+    public String toAsm() {
+        return "leave";
+    }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Mnemonic.java

@@ -0,0 +1,6 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public abstract class Mnemonic {
+  public abstract String toAsm();
+  public int indentation = 2;
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Mov.java

@@ -0,0 +1,40 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Mov extends TwoOperandMnemonic{
+  public String dataType = "q";
+
+  public Mov(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  public Mov(String dataType, String label, String src, String dst) {
+    this.dataType = dataType;
+    this.src = label + "(" + src + ")";
+    this.dst = dst;
+  }
+
+  public Mov(String dataType, int offset, String src, String dst) {
+    this.dataType = dataType;
+    this.src = offset + "(" + src + ")";
+    this.dst = dst;
+  }
+
+  public Mov(String dataType, int immediate, String dst) {
+    this.dataType = dataType;
+    this.src = "$" + immediate;
+    this.dst = dst;
+  }
+
+  public Mov(String dataType, String src, int offset, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = offset + "(" + dst + ")";
+  }
+
+  @Override
+  public String toAsm() {
+    return "mov" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Mul.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Mul extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Mul(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "mul" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Neg.java

@@ -0,0 +1,14 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Neg extends OneOperandMnemonic {
+
+  public Neg(String operand) {
+    this.operand = operand;
+  }
+
+  @Override
+  public String toAsm() {
+    return "neg " + this.operand;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Newline.java

@@ -0,0 +1,9 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Newline extends NoOperandMnemonic {
+
+  @Override
+  public String toAsm() {
+    return "";
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/NoOperandMnemonic.java

@@ -0,0 +1,5 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public abstract class NoOperandMnemonic extends Mnemonic {
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/OneOperandMnemonic.java

@@ -0,0 +1,5 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public abstract class OneOperandMnemonic extends Mnemonic {
+  public String operand;
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Pop.java

@@ -0,0 +1,16 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Pop extends OneOperandMnemonic {
+  public String dataType;
+
+  public Pop(String dataType, String operand) {
+    this.dataType = dataType;
+    this.operand = operand;
+  }
+
+  @Override
+  public String toAsm() {
+    return "pop" + this.dataType + " " + this.operand;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Push.java

@@ -0,0 +1,21 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Push extends OneOperandMnemonic {
+  public String dataType;
+
+  public Push(String dataType, int immediate){
+    this.dataType = dataType;
+    this.operand = "$" + immediate;
+  }
+
+  public Push(String dataType, String operand) {
+    this.dataType = dataType;
+    this.operand = operand;
+  }
+
+  @Override
+  public String toAsm() {
+    return "push" + this.dataType + " " + this.operand;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Ret.java

@@ -0,0 +1,8 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Ret extends NoOperandMnemonic {
+  @Override
+  public String toAsm() {
+    return "ret";
+  }
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Sub.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Sub extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Sub(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "sub" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Text.java

@@ -0,0 +1,15 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Text extends NoOperandMnemonic {
+  public String text;
+
+  public Text(String text) {
+    this.text = text;
+    this.indentation = 0;
+  }
+
+  @Override
+  public String toAsm() {
+    return this.text;
+  }  
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/TwoOperandMnemonic.java

@@ -0,0 +1,6 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public abstract class TwoOperandMnemonic extends Mnemonic {
+  public String src;
+  public String dst;
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Ucomi.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Ucomi extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Ucomi(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "ucomi" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/asm/mnemonics/Xor.java

@@ -0,0 +1,17 @@
+package de.hsrm.compiler.Klang.asm.mnemonics;
+
+public class Xor extends TwoOperandMnemonic {
+  public String dataType;
+
+  public Xor(String dataType, String src, String dst) {
+    this.dataType = dataType;
+    this.src = src;
+    this.dst = dst;
+  }
+
+  @Override
+  public String toAsm() {
+    return "xor" + this.dataType + " " + this.src + ", " + this.dst;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/helper/FunctionInformation.java

@@ -1,19 +0,0 @@
-package de.hsrm.compiler.Klang.helper;
-
-import java.util.Map;
-
-import de.hsrm.compiler.Klang.types.Type;
-
-public class FunctionInformation {
-  public String name;
-  public Type returnType;
-  public Map<String, Type> parameters;
-  public Type[] signature;
-
-  public FunctionInformation(String name, Type returnType, Map<String,Type> parameters, Type[] signature) {
-    this.name = name;
-    this.returnType = returnType;
-    this.parameters = parameters;
-    this.signature = signature;
-  }  
-}

src/main/java/de/hsrm/compiler/Klang/nodes/EnumDefinition.java

@@ -0,0 +1,19 @@
+package de.hsrm.compiler.Klang.nodes;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class EnumDefinition extends Node {
+
+    public String name;
+    public EnumValue[] enums;
+
+    public EnumDefinition(String name, EnumValue[] enums) {
+        this.name = name;
+        this.enums = enums;
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}

src/main/java/de/hsrm/compiler/Klang/nodes/EnumValue.java

@@ -0,0 +1,18 @@
+package de.hsrm.compiler.Klang.nodes;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class EnumValue  extends Node {
+    public String value;
+    public int index;
+
+    public EnumValue(String value, int index) {
+        this.value = value;
+        this.index = index;
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}

src/main/java/de/hsrm/compiler/Klang/nodes/FunctionDefinition.java

@@ -1,17 +1,20 @@
 package de.hsrm.compiler.Klang.nodes;
 
+import de.hsrm.compiler.Klang.nodes.statements.VariableDeclaration;
 import de.hsrm.compiler.Klang.visitors.Visitor;
 
 public class FunctionDefinition extends Node {
 
   public String name;
   public Parameter[] parameters;
+  public VariableDeclaration[] localVariables;
   public Block block;
 
-  public FunctionDefinition(String name, Parameter[] parameters, Block block) {
+  public FunctionDefinition(String name, Parameter[] parameters, VariableDeclaration[] localVariables, Block block) {
     this.name = name;
     this.parameters = parameters;
     this.block = block;
+    this.localVariables = localVariables;
   }
 
   @Override

src/main/java/de/hsrm/compiler/Klang/nodes/Program.java

@@ -9,11 +9,18 @@ public class Program extends Node {
   
   public FunctionDefinition[] funcs;
   public Map<String, StructDefinition> structs;
+  public Map<String, EnumDefinition> enums;
   public Expression expression;
 
-  public Program(FunctionDefinition[] funcs, Map<String, StructDefinition> structs, Expression expression) {
+  public Program(
+          FunctionDefinition[] funcs,
+          Map<String, StructDefinition> structs,
+          Map<String, EnumDefinition> enums,
+          Expression expression
+  ) {
     this.funcs = funcs;
     this.structs = structs;
+    this.enums = enums;
     this.expression = expression;
   }
 

src/main/java/de/hsrm/compiler/Klang/nodes/expressions/EnumAccessExpression.java

@@ -0,0 +1,26 @@
+package de.hsrm.compiler.Klang.nodes.expressions;
+
+import de.hsrm.compiler.Klang.nodes.EnumDefinition;
+import de.hsrm.compiler.Klang.nodes.EnumValue;
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class EnumAccessExpression extends Expression {
+    public String enumName;
+    public String enumValueName;
+    public EnumValue enumValue;
+
+    public EnumAccessExpression(
+            String enumName,
+            String enumValueName,
+            EnumValue enumValue
+    ) {
+        this.enumName = enumName;
+        this.enumValueName = enumValueName;
+        this.enumValue = enumValue;
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}

src/main/java/de/hsrm/compiler/Klang/nodes/expressions/MemberAccessExpression.java

@@ -2,12 +2,12 @@ package de.hsrm.compiler.Klang.nodes.expressions;
 
 import de.hsrm.compiler.Klang.visitors.Visitor;
 
-public class StructFieldAccessExpression extends Expression {
+public class MemberAccessExpression extends Expression {
   public String varName;
   public String structName;
   public String[] path;
 
-  public StructFieldAccessExpression(String varName, String structName, String[] path) {
+  public MemberAccessExpression(String varName, String structName, String[] path) {
     this.varName = varName;
     this.structName = structName;
     this.path = path;

src/main/java/de/hsrm/compiler/Klang/nodes/statements/ReturnStatement.java

@@ -11,6 +11,10 @@ public class ReturnStatement extends Statement {
         this.expression = expression;
     }
 
+    public ReturnStatement() {
+      this.expression = null;    
+    }
+
     @Override
     public <R> R welcome(Visitor<R> v) {
         return v.visit(this);

src/main/java/de/hsrm/compiler/Klang/types/BooleanType.java

@@ -1,5 +1,7 @@
 package de.hsrm.compiler.Klang.types;
 
+import de.hsrm.compiler.Klang.Value;
+
 public class BooleanType extends PrimitiveType {
 
   private static BooleanType instance = null;
@@ -30,7 +32,11 @@ public class BooleanType extends PrimitiveType {
     }
 
     // Every remaining type will throw a RuntimeException
-    throw new RuntimeException("Type missmatch: cannot combine " + this.getName() + " and " + that.getName());
+    throw new RuntimeException("Type mismatch: cannot combine " + this.getName() + " and " + that.getName());
   }
 
+  @Override
+  public boolean valuesEqual(Value a, Value b) {
+    return a.asBoolean() == b.asBoolean();
+  }
 }

src/main/java/de/hsrm/compiler/Klang/types/FloatType.java

@@ -1,5 +1,7 @@
 package de.hsrm.compiler.Klang.types;
 
+import de.hsrm.compiler.Klang.Value;
+
 public class FloatType extends NumericType {
 
   private static FloatType instance = null;
@@ -34,7 +36,11 @@ public class FloatType extends NumericType {
     }
 
     // Every remaining type will throw a RuntimeException
-    throw new RuntimeException("Type missmatch: cannot combine " + this.getName() + " and " + that.getName());
+    throw new RuntimeException("Type mismatch: cannot combine " + this.getName() + " and " + that.getName());
   }
 
+  @Override
+  public boolean valuesEqual(Value a, Value b) {
+    return a.asFloat() == b.asFloat();
+  }
 }

src/main/java/de/hsrm/compiler/Klang/types/IntegerType.java

@@ -1,5 +1,7 @@
 package de.hsrm.compiler.Klang.types;
 
+import de.hsrm.compiler.Klang.Value;
+
 public class IntegerType extends NumericType {
 
   private static IntegerType instance = null;
@@ -34,7 +36,12 @@ public class IntegerType extends NumericType {
     }
 
     // Every remaining type will throw a RuntimeException
-    throw new RuntimeException("Type missmatch: cannot combine " + this.getName() + " and " + that.getName());
+    throw new RuntimeException("Type mismatch: cannot combine " + this.getName() + " and " + that.getName());
+  }
+
+  @Override
+  public boolean valuesEqual(Value a, Value b) {
+    return a.asInteger() == b.asInteger();
   }
 
 }

src/main/java/de/hsrm/compiler/Klang/types/NamedType.java

@@ -0,0 +1,53 @@
+package de.hsrm.compiler.Klang.types;
+
+import de.hsrm.compiler.Klang.Value;
+
+public class NamedType extends Type {
+    public String name;
+
+    public NamedType(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public Type combine(Type that) {
+        if(this.equals(that) || (that instanceof NullType)) {
+            return this;
+        }
+
+        throw new RuntimeException("Type mismatch: cannot combine " + getName() + " and " + that.getName());
+    }
+
+    @Override
+    public boolean valuesEqual(Value a, Value b) {
+        return a.asObject().equals(b.asObject());
+    }
+
+    @Override
+    public boolean isPrimitiveType() {
+        return false;
+    }
+
+    @Override
+    public boolean isNumericType() {
+        return false;
+    }
+
+    @Override
+    public boolean equals(Object that) {
+        if (this == that) {
+            return true;
+        }
+
+        if (that instanceof NamedType thatType) {
+            return getName().equals(thatType.getName());
+        }
+
+        return false;
+    }
+}

src/main/java/de/hsrm/compiler/Klang/types/NullType.java

@@ -1,5 +1,7 @@
 package de.hsrm.compiler.Klang.types;
 
+import de.hsrm.compiler.Klang.Value;
+
 public class NullType extends Type {
 
     private static NullType instance = null;
@@ -21,13 +23,18 @@ public class NullType extends Type {
     public Type combine(Type that) {
         // You can not combine null with a primitive type
         if (that.isPrimitiveType()) {
-            throw new RuntimeException("Type missmatch: cannot combine " + this.getName() + " and " + that.getName());
+            throw new RuntimeException("Type mismatch: cannot combine " + this.getName() + " and " + that.getName());
         }
 
         // Everything else combines with null to the type it was before
         return that;
     }
 
+    @Override
+    public boolean valuesEqual(Value a, Value b) {
+        return a.asObject() == b.asObject();
+    }
+
     @Override
     public boolean isPrimitiveType() {
         return false;

src/main/java/de/hsrm/compiler/Klang/types/StructType.java

@@ -1,54 +0,0 @@
-package de.hsrm.compiler.Klang.types;
-
-public class StructType extends Type {
-
-    public String name;
-
-    public StructType(String name) {
-        this.name = name;
-    }
-
-    @Override
-    public String getName() {
-        return this.name;
-    }
-
-    @Override
-    public Type combine(Type that) {
-        if (that.equals(this)) {
-            return this;
-        }
-
-        // If you combine a null type with a struct type, you
-        // always get the struct type back. 
-        if (that == NullType.getType()) {
-            return this;
-        }
-
-        throw new RuntimeException("Type missmatch: cannot combine " + this.getName() + " and " + that.getName());
-    }
-
-    @Override
-    public boolean isPrimitiveType() {
-        return false;
-    }
-
-    @Override
-    public boolean equals(Object that) {
-        if (this == that) {
-            return true;
-        }
-
-        if (that instanceof StructType) {
-            StructType thatType = (StructType) that;
-            return this.getName().equals(thatType.getName());
-        }
-
-        return false;
-    }
-
-    @Override
-    public boolean isNumericType() {
-        return false;
-    }
-}

src/main/java/de/hsrm/compiler/Klang/types/Type.java

@@ -1,5 +1,12 @@
 package de.hsrm.compiler.Klang.types;
 
+import de.hsrm.compiler.Klang.Value;
+import de.hsrm.compiler.Klang.nodes.EnumDefinition;
+import de.hsrm.compiler.Klang.nodes.FunctionDefinition;
+import de.hsrm.compiler.Klang.nodes.StructDefinition;
+
+import java.util.Map;
+
 public abstract class Type {
 
   // Returns an instance of IntegerType
@@ -20,18 +27,24 @@ public abstract class Type {
     return NullType.getType();
   }
 
+  public static VoidType getVoidType() {
+    return VoidType.getType();
+  }
+
   public static Type getByName(String name) {
     switch (name) {
       case "bool": return getBooleanType();
       case "int": return getIntegerType();
       case "float": return getFloatType();
       case "null": return getNullType();
-      default: return new StructType(name);
+      case "void": return getVoidType();
+      default: return new NamedType(name);
     }
   }
 
   public abstract String getName();
   public abstract Type combine(Type that);
+  public abstract boolean valuesEqual(Value a, Value b);
   public abstract boolean isPrimitiveType();
   public abstract boolean isNumericType();
-}
+}

src/main/java/de/hsrm/compiler/Klang/types/VoidType.java

@@ -0,0 +1,45 @@
+package de.hsrm.compiler.Klang.types;
+
+import de.hsrm.compiler.Klang.Value;
+
+public class VoidType extends Type {
+
+  private static VoidType instance;
+
+  public static VoidType getType() {
+    if (instance != null) {
+        return instance;
+    }
+    instance = new VoidType();
+    return instance;
+}
+
+  @Override
+  public String getName() {
+    return "void";
+  }
+
+  @Override
+  public Type combine(Type that) {
+    if (that.equals(this)) {
+      return this;
+    }
+    throw new RuntimeException("Type mismatch: cannot combine " + this.getName() + " and " + that.getName());
+  }
+
+  @Override
+  public boolean valuesEqual(Value a, Value b) {
+    throw new RuntimeException("Can not compare void types.");
+  }
+
+  @Override
+  public boolean isPrimitiveType() {
+    return false;
+  }
+
+  @Override
+  public boolean isNumericType() {
+    return false;
+  }
+
+}

src/main/java/de/hsrm/compiler/Klang/visitors/EvalVisitor.java

@@ -4,17 +4,14 @@ import java.util.HashMap;
 import java.util.Map;
 
 import de.hsrm.compiler.Klang.Value;
-import de.hsrm.compiler.Klang.nodes.Block;
-import de.hsrm.compiler.Klang.nodes.FunctionDefinition;
-import de.hsrm.compiler.Klang.nodes.Parameter;
-import de.hsrm.compiler.Klang.nodes.Program;
-import de.hsrm.compiler.Klang.nodes.StructDefinition;
-import de.hsrm.compiler.Klang.nodes.StructField;
+import de.hsrm.compiler.Klang.nodes.*;
 import de.hsrm.compiler.Klang.nodes.expressions.*;
 import de.hsrm.compiler.Klang.nodes.loops.DoWhileLoop;
 import de.hsrm.compiler.Klang.nodes.loops.ForLoop;
 import de.hsrm.compiler.Klang.nodes.loops.WhileLoop;
 import de.hsrm.compiler.Klang.nodes.statements.*;
+import de.hsrm.compiler.Klang.types.NamedType;
+import de.hsrm.compiler.Klang.types.NullType;
 import de.hsrm.compiler.Klang.types.Type;
 
 public class EvalVisitor implements Visitor<Value> {
@@ -51,25 +48,11 @@ public class EvalVisitor implements Visitor<Value> {
 
   @Override
   public Value visit(EqualityExpression e) {
-    Value lhs = e.lhs.welcome(this);
-    Value rhs = e.rhs.welcome(this);
-    Type resultType = Type.getBooleanType();
-    Type combineType = lhs.type.combine(rhs.type);
+    var lhs = e.lhs.welcome(this);
+    var rhs = e.rhs.welcome(this);
+    var combinedType = lhs.type.combine(rhs.type);
 
-    switch(combineType.getName()) {
-      case "bool": {
-        return new Value(lhs.asBoolean() == rhs.asBoolean(), resultType);
-      }
-      case "int": {
-        return new Value(lhs.asInteger() == rhs.asInteger(), resultType);
-      }
-      case "float": {
-        return new Value(lhs.asFloat() == rhs.asFloat(), resultType);
-      }
-      default: {
-        return new Value(lhs.asObject() == rhs.asObject(), resultType);
-      }
-    }
+    return new Value(combinedType.valuesEqual(lhs, rhs), Type.getBooleanType());
   }
 
   @Override
@@ -413,13 +396,16 @@ public class EvalVisitor implements Visitor<Value> {
 
   @Override
   public Value visit(ReturnStatement e) {
+    if (e.expression == null) {
+      return new Value(null, Type.getVoidType());
+    }
     return e.expression.welcome(this);
   }
 
   @Override
   public Value visit(Block e) {
     for (var stmt : e.statements) {
-      Value result = stmt.welcome(this);
+      var result = stmt.welcome(this);
       if (result != null) {
         return result;
       }
@@ -447,7 +433,7 @@ public class EvalVisitor implements Visitor<Value> {
     this.env = newEnv;
 
     // Execute
-    Value result = func.block.welcome(this);
+    var result = func.block.welcome(this);
 
     // Das alte env wiederherstellen
     this.env = oldEnv;
@@ -471,6 +457,16 @@ public class EvalVisitor implements Visitor<Value> {
     return null;
   }
 
+  @Override
+  public Value visit(EnumDefinition e) {
+    return null;
+  }
+
+  @Override
+  public Value visit(EnumValue e) {
+    return null;
+  }
+
   @Override
   public Value visit(StructDefinition e) {
     // We get these from a previous visitor
@@ -484,7 +480,7 @@ public class EvalVisitor implements Visitor<Value> {
   }
 
   @Override
-  public Value visit(StructFieldAccessExpression e) {
+  public Value visit(MemberAccessExpression e) {
     Value var = this.env.get(e.varName);
     Map<String, Value> struct = var.asStruct();
 
@@ -496,6 +492,11 @@ public class EvalVisitor implements Visitor<Value> {
     return currentValue;
   }
 
+  @Override
+  public Value visit(EnumAccessExpression e) {
+    return new Value(e.enumValueName, e.type);
+  }
+
   @Override
   public Value visit(ConstructorCall e) {
     StructDefinition structDef = this.structs.get(e.structName);
@@ -506,12 +507,17 @@ public class EvalVisitor implements Visitor<Value> {
       struct.put(structDef.fields[i].name, arg);
     }
 
-    return new Value(struct);
+    var structValue = new Value(struct);
+    structValue.type = structDef.type;
+
+    return structValue;
   }
 
   @Override
   public Value visit(NullExpression e) {
-    return null;
+    var nullValue = new Value(null);
+    nullValue.type = new NullType();
+    return nullValue;
   }
 
   @Override

src/main/java/de/hsrm/compiler/Klang/visitors/GetVars.java

@@ -194,7 +194,9 @@ class GetVars implements Visitor<Void> {
 
   @Override
   public Void visit(ReturnStatement e) {
-    e.expression.welcome(this);
+    if (e.expression != null) {
+      e.expression.welcome(this);
+    }
     return null;
   }
 
@@ -234,6 +236,16 @@ class GetVars implements Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visit(EnumDefinition e) {
+    return null;
+  }
+
+  @Override
+  public Void visit(EnumValue e) {
+    return null;
+  }
+
   @Override
   public Void visit(StructDefinition e) {
     return null;
@@ -245,7 +257,12 @@ class GetVars implements Visitor<Void> {
   }
 
   @Override
-  public Void visit(StructFieldAccessExpression e) {
+  public Void visit(MemberAccessExpression e) {
+    return null;
+  }
+
+  @Override
+  public Void visit(EnumAccessExpression e) {
     return null;
   }
 

src/main/java/de/hsrm/compiler/Klang/visitors/PrettyPrintVisitor.java

@@ -68,6 +68,12 @@ public class PrettyPrintVisitor implements Visitor<Void> {
       ex.nl();
     }
 
+    for (var enumDef: e.enums.values()) {
+      enumDef.welcome(this);
+      ex.nl();
+      ex.nl();
+    }
+
     e.expression.welcome(this);
     ex.write(";");
     return null;
@@ -304,8 +310,11 @@ public class PrettyPrintVisitor implements Visitor<Void> {
 
   @Override
   public Void visit(ReturnStatement e) {
-    ex.write("return ");
-    e.expression.welcome(this);
+    ex.write("return");
+    if (e.expression != null) {
+      ex.write(" ");
+      e.expression.welcome(this);
+    }
     ex.write(";");
     return null;
   }
@@ -377,6 +386,28 @@ public class PrettyPrintVisitor implements Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visit(EnumDefinition e) {
+    ex.write("enum " + e.name + " { ");
+    var first = true;
+    for(var enumValue: e.enums) {
+      if (!first) {
+        ex.write(", ");
+      } else {
+        first = false;
+      }
+      enumValue.welcome(this);
+    }
+    ex.write(" }");
+    return null;
+  }
+
+  @Override
+  public Void visit(EnumValue e) {
+    ex.write(e.value);
+    return null;
+  }
+
   @Override
   public Void visit(StructDefinition e) {
     ex.write("struct " + e.name + " {");
@@ -398,7 +429,7 @@ public class PrettyPrintVisitor implements Visitor<Void> {
   }
 
   @Override
-  public Void visit(StructFieldAccessExpression e) {
+  public Void visit(MemberAccessExpression e) {
     ex.write(e.varName);
     for (int i = 0; i < e.path.length; i++) {
       ex.write(".");
@@ -407,6 +438,15 @@ public class PrettyPrintVisitor implements Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visit(EnumAccessExpression e) {
+    ex.write(e.enumName);
+    ex.write(".");
+    ex.write(e.enumValueName);
+
+    return null;
+  }
+
   @Override
   public Void visit(ConstructorCall e) {
     ex.write("create " + e.structName + "(");

src/main/java/de/hsrm/compiler/Klang/visitors/Visitor.java

@@ -1,11 +1,6 @@
 package de.hsrm.compiler.Klang.visitors;
 
-import de.hsrm.compiler.Klang.nodes.Block;
-import de.hsrm.compiler.Klang.nodes.FunctionDefinition;
-import de.hsrm.compiler.Klang.nodes.Parameter;
-import de.hsrm.compiler.Klang.nodes.Program;
-import de.hsrm.compiler.Klang.nodes.StructDefinition;
-import de.hsrm.compiler.Klang.nodes.StructField;
+import de.hsrm.compiler.Klang.nodes.*;
 import de.hsrm.compiler.Klang.nodes.expressions.*;
 import de.hsrm.compiler.Klang.nodes.loops.*;
 import de.hsrm.compiler.Klang.nodes.statements.*;
@@ -42,9 +37,12 @@ public interface Visitor<R> {
     R visit(FunctionCall e);
     R visit(Program e);
     R visit(Parameter e);
+    R visit(EnumDefinition e);
+    R visit(EnumValue e);
     R visit(StructDefinition e);
     R visit(StructField e);
-    R visit(StructFieldAccessExpression e);
+    R visit(MemberAccessExpression e);
+    R visit(EnumAccessExpression e);
     R visit(ConstructorCall e);
     R visit(NullExpression e);
     R visit(DestructorCall e);

src/test/java/AndTest.java

@@ -12,7 +12,8 @@ public class AndTest {
         ParseTree tree = Helper.prepareParser("function foo(): bool { return 1 && 2; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:30 && is only defined for bool.", e.getMessage());

src/test/java/ConstructorCallTest.java

@@ -13,18 +13,20 @@ public class ConstructorCallTest {
         ParseTree tree = Helper.prepareParser("struct bar { a: int; } function foo(): bar { return create schwurbel(1); } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:52 Struct with name \"schwurbel\" not defined.", e.getMessage());
     }
 
     @Test
-    void numConstructorParameterMissmatch() {
+    void numConstructorParametermismatch() {
         ParseTree tree = Helper.prepareParser("struct bar { a: int; } function foo(): bar { return create bar(1, false); } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:52 Struct \"bar\" defined 1 fields, but got 2 constructor parameters.", e.getMessage());
@@ -35,9 +37,10 @@ public class ConstructorCallTest {
         ParseTree tree = Helper.prepareParser("struct bar { a: int; } function foo(): bar { return create bar(false); } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:63 argument 0 Type missmatch: cannot combine bool and int", e.getMessage());
+        assertEquals("Error in line 1:63 argument 0 Type mismatch: cannot combine bool and int", e.getMessage());
     }
 }

src/test/java/DestroyStatementTest.java

@@ -13,9 +13,10 @@ public class DestroyStatementTest {
         ParseTree tree = Helper.prepareParser("struct bar { a: int; } function foo(): int { destroy x; return 1; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:45 Variable with name \"x\" not defined.", e.getMessage());
+        assertEquals("Error in line 1:45 Variable or parameter with name \"x\" not defined.", e.getMessage());
     }
 }

src/test/java/FieldAssignmentTest.java

@@ -13,10 +13,11 @@ public class FieldAssignmentTest {
         ParseTree tree = Helper.prepareParser("struct test { a: int; } function foo(): int { str.a = 1; return 1; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:46 Variable with name str not defined.", e.getMessage());
+        assertEquals("Error in line 1:46 Variable or parameter with name \"str\" not defined.", e.getMessage());
     }
 
     @Test
@@ -24,9 +25,10 @@ public class FieldAssignmentTest {
         ParseTree tree = Helper.prepareParser("struct test { a: int; } function foo(): int { let x: int = 0; x.a = 0; return 1; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:62 Variable must reference a struct but references int.", e.getMessage());
+        assertEquals("Error in line 1:62 Variable or parameter must reference a struct but references int.", e.getMessage());
     }
 }

src/test/java/FunctionCallTest.java

@@ -13,7 +13,8 @@ public class FunctionCallTest {
         ParseTree tree = Helper.prepareParser("function foo(): int { return 1; } bar();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:34 Function with name \"bar\" not defined.", e.getMessage());
@@ -24,18 +25,20 @@ public class FunctionCallTest {
         ParseTree tree = Helper.prepareParser("function foo(): int { return 1; } foo(5);");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:34 Function \"foo\" expects 0 parameters, but got 1.", e.getMessage());
     }
 
     @Test
-    void parameterTypeMissmatch() {
+    void parameterTypeMismatch() {
         ParseTree tree = Helper.prepareParser("function foo(x: int): int { return x; } foo(false);");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:40 argument 0 Expected int but got: bool", e.getMessage());

src/test/java/FunctionDefinitionTest.java

@@ -1,32 +1,119 @@
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-
-import org.antlr.v4.runtime.tree.ParseTree;
+import de.hsrm.compiler.Klang.ContextAnalysis;
 import org.junit.jupiter.api.Test;
 
-import de.hsrm.compiler.Klang.ContextAnalysis;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class FunctionDefinitionTest {
 
     @Test
-    void typeNotDefined() {
-        ParseTree tree = Helper.prepareParser("function foo(): schwurbel { return 1; } foo();");
-        var funcs = Helper.getFuncs(tree);
-        var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
-        
-        Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:0 Type schwurbel not defined.", e.getMessage());
+    void shouldNotThrowIfReturnTypeIsReferringToAnEnum() {
+        // given
+        var tree = Helper.prepareParser(" enum bar {A,B,C} function foo(a: int): bar { return bar.A; } foo(1);");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
     }
 
     @Test
-    void noReturnExpression() {
-        ParseTree tree = Helper.prepareParser("function foo(): int { let x: int; x = 0; } foo();");
-        var funcs = Helper.getFuncs(tree);
-        var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
-        
-        Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:0 Function foo has to return something of type int.", e.getMessage());
+    void shouldNotThrowIfParameterTypeIsReferringToAnEnum() {
+        // given
+        var tree = Helper.prepareParser(" enum bar {A,B,C} function foo(a: bar): int { return 1; } foo(bar.A);");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldThrowExceptionIfParameterTypeIsNotDefined() {
+        // given
+        var tree = Helper.prepareParser("function foo(a: schwurbel): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:14 Type schwurbel not defined.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfReturnTypeIsNotDefined() {
+        // given
+        var tree = Helper.prepareParser("function foo(): schwurbel { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:14 Type schwurbel not defined.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfReturnStatementIsMissing() {
+        // given
+        var tree = Helper.prepareParser("function foo(): int { let x: int; x = 0; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:20 Function foo has to return something of type int.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfParameterNameMatchesEnumName() {
+        // given
+        var tree = Helper.prepareParser("enum Bar { A, B } function foo(Bar: int): int { return 1; } foo(1);");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:31 Parameter name Bar duplicates an enum of the same name.", e.getMessage());
+    }
+
+    @Test
+    void shouldResetVariablesAndParameterEnvironment() {
+        // given
+        var tree = Helper.prepareParser("""
+                function foo(x: int): int {
+                  return 1;
+                }
+                function bar(): int {
+                  let x: int = 0;
+                  return x;
+                }
+                                
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
     }
 }

src/test/java/Helper.java

@@ -16,21 +16,21 @@ public class Helper {
         return parser.parse();
     }
 
-    public static Map<String, FunctionInformation> getFuncs(ParseTree tree) {
-        var functionDefinitions = new HashMap<String, FunctionInformation>();
-        new GetFunctions(functionDefinitions).visit(tree);
+    public static Map<String, FunctionDefinition> getFuncs(ParseTree tree) {
+        var functionDefinitions = new HashMap<String, FunctionDefinition>();
+        new GetDefinitions(functionDefinitions, new HashMap<>(), new HashMap<>()).visit(tree);
         return functionDefinitions;
     }
 
-    public static Set<String> getStructNames(ParseTree tree) {
-        var structNames = new HashSet<String>();
-        new GetStructNames(structNames).visit(tree);
-        return structNames;
-    }
-
     public static Map<String, StructDefinition> getStructs(ParseTree tree) {
         var structs = new HashMap<String, StructDefinition>();
-        new GetStructs(getStructNames(tree), structs).visit(tree);
+        new GetDefinitions(new HashMap<>(), structs, new HashMap<>()).visit(tree);
         return structs;
     }
+
+    public static Map<String, EnumDefinition> getEnums(ParseTree tree) {
+        var enums = new HashMap<String, EnumDefinition>();
+        new GetDefinitions(new HashMap<>(), new HashMap<>(), enums).visit(tree);
+        return enums;
+    }
 }

src/test/java/ModuloTest.java

@@ -12,7 +12,8 @@ public class ModuloTest {
         ParseTree tree = Helper.prepareParser("function foo(): float { return 1.0 % 2.3; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:31 Only integers are allowed for modulo.", e.getMessage());

src/test/java/NaughtTest.java

@@ -0,0 +1,72 @@
+import de.hsrm.compiler.Klang.ContextAnalysis;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class NaughtTest {
+    @Test
+    void shouldBeComparableToStruct() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): int {
+                        let a: bar = create bar(1);
+                        if (a == naught) {
+                            return -1;
+                        }
+                        return 1;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldBeAssignableToStruct() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): int {
+                        let a: bar = naught;
+                        return 1;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldBeReturnable() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): bar {
+                        return naught;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+}

src/test/java/OrTest.java

@@ -13,7 +13,8 @@ public class OrTest {
         ParseTree tree = Helper.prepareParser("function foo(): bool { return 1 || 2; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:30 || is only defined for bool.", e.getMessage());

src/test/java/ParameterTest.java

@@ -1,14 +0,0 @@
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-
-import org.antlr.v4.runtime.tree.ParseTree;
-import org.junit.jupiter.api.Test;
-
-public class ParameterTest {
-    @Test
-    void typeNotDefined() {
-        ParseTree tree = Helper.prepareParser("struct test { a: schwurbel; } function foo(): int { return 1; } foo();");
-        Exception e = assertThrows(RuntimeException.class, () -> Helper.getStructs(tree));
-        assertEquals("Error in line 1:14 Type schwurbel not defined.", e.getMessage());
-    }
-}

src/test/java/StructDefinitionTest.java

@@ -0,0 +1,94 @@
+import de.hsrm.compiler.Klang.ContextAnalysis;
+import de.hsrm.compiler.Klang.GetDefinitions;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class StructDefinitionTest {
+    @Test
+    void shouldNotThrowIfStructIsWellDefined() {
+        // given
+        var tree = Helper.prepareParser("struct test { a: int; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfStructFieldTypeIsReferringToEnum() {
+        // given
+        var tree = Helper.prepareParser("struct test { a: bar; } enum bar {A,B,C} function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfStructFieldTypeIsReferringToStruct() {
+        // given
+        var tree = Helper.prepareParser("struct a { hello: int; } struct b { world: a; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldThrowExceptionIfStructFieldNameShadowsAStruct() {
+        // given
+        var tree = Helper.prepareParser("struct bar { a: int; } struct baz { bar: int; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:36 Struct field name bar shadows a struct of the same name.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfStructFieldNameShadowsAnEnum() {
+        // given
+        var tree = Helper.prepareParser("enum bar { A, B } struct baz { bar: int; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:31 Struct field name bar shadows an enum of the same name.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfStructFieldTypeIsNotDefined() {
+        // given
+        var tree = Helper.prepareParser("struct test { a: schwurbel; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:14 Type schwurbel not defined.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfStructFieldTypeIsReferringToAFunction() {
+        // given
+        var tree = Helper.prepareParser("struct test { a: foo; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:14 Type foo not defined.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfStructFieldNameIsDuplicated() {
+        // given
+        var tree = Helper.prepareParser("struct test { a: int; a: bool; } function foo(): int { return 1; } foo();");
+        var getDefs = new GetDefinitions(new HashMap<>(), new HashMap<>(), new HashMap<>());
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> getDefs.visit(tree));
+        assertEquals("Error in line 1:22 Duplicate struct field a in struct test.", e.getMessage());
+    }
+}

src/test/java/StructFieldAccessTest.java

@@ -12,10 +12,11 @@ public class StructFieldAccessTest {
         ParseTree tree = Helper.prepareParser("struct test { a: int; } function foo(): int { return str.a; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:53 Variable with name str not defined.", e.getMessage());
+        assertEquals("Error in line 1:53 Variable or parameter with name \"str\" not defined.", e.getMessage());
     }
 
     @Test
@@ -23,9 +24,10 @@ public class StructFieldAccessTest {
         ParseTree tree = Helper.prepareParser("struct test { a: int; } function foo(): int { let x: int = 0; return x.a; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:69 Variable must reference a struct but references int.", e.getMessage());
+        assertEquals("Error in line 1:69 Variable or parameter must reference a struct but references int.", e.getMessage());
     }
 }

src/test/java/VariableAssignmentTest.java

@@ -13,9 +13,10 @@ public class VariableAssignmentTest {
         ParseTree tree = Helper.prepareParser("function foo(): int { x = 1; return 1; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:22 Variable with name \"x\" not defined.", e.getMessage());
+        assertEquals("Error in line 1:22 Variable or parameter with name \"x\" not defined.", e.getMessage());
     }
 }

src/test/java/VariableDeclarationTest.java

@@ -1,32 +1,109 @@
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-
-import org.antlr.v4.runtime.tree.ParseTree;
+import de.hsrm.compiler.Klang.ContextAnalysis;
 import org.junit.jupiter.api.Test;
 
-import de.hsrm.compiler.Klang.ContextAnalysis;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class VariableDeclarationTest {
     @Test
-    void typeNotDefined() {
-        ParseTree tree = Helper.prepareParser("function foo(): int { let X: unk; return 1; } foo();");
-        var funcs = Helper.getFuncs(tree);
-        var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
-        
-        Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+    void shouldNotThrowIfDeclaredTypeIsAStruct() {
+        // given
+        var tree = Helper.prepareParser("struct bar { a: int; } function foo(): int { let a: bar; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfDeclaredTypeIsAnEnum() {
+        // given
+        var tree = Helper.prepareParser("enum bar { A, B } function foo(): int { let a: bar = bar.A; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldThrowExceptionIfDeclaredNameShadowsEnumName() {
+        // given
+        var tree = Helper.prepareParser("enum bar { A, B } function foo(): int { let bar: int; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:40 Variable name bar shadows an enum of the same name.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfDeclaredNameShadowsStruct() {
+        // given
+        var tree = Helper.prepareParser("struct bar { a: int; } function foo(): int { let bar: int; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:45 Variable name bar shadows a struct of the same name.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfDeclaredTypeIsNotDefined() {
+        // given
+        var tree = Helper.prepareParser("function foo(): int { let X: unk; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:22 Type unk not defined.", e.getMessage());
     }
 
     @Test
-    void variableRedeclaration()
-    {
-        ParseTree tree = Helper.prepareParser("function foo(): int { let x: int; let x: bool; return 1; } foo();");
-        var funcs = Helper.getFuncs(tree);
-        var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
-        
-        Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:34 Redeclaration of variable with name \"x\".", e.getMessage());
+    void shouldThrowExceptionIfVariableIsRedeclared() {
+        // given
+        var tree = Helper.prepareParser("function foo(): int { let x: int; let x: bool; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:34 Redeclaration of variable or parameter with name \"x\".", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowExceptionIfVariableReferencesEnumButIsNotInitialized() {
+        // given
+        var tree = Helper.prepareParser("enum bar { A, B } function foo(): int { let x: bar; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:40 Variable x references an enum but is not initialized.", e.getMessage());
     }
 }

src/test/java/VariableTest.java

@@ -13,10 +13,11 @@ public class VariableTest {
         ParseTree tree = Helper.prepareParser("function foo(): int { return x; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:29 Variable with name \"x\" not defined.", e.getMessage());
+        assertEquals("Error in line 1:29 Variable or parameter with name \"x\" not defined.", e.getMessage());
     }
 
     @Test
@@ -24,7 +25,8 @@ public class VariableTest {
         ParseTree tree = Helper.prepareParser("function foo(): int { let x: int; return x; } foo();");
         var funcs = Helper.getFuncs(tree);
         var structs = Helper.getStructs(tree);
-        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs);
+        var enums = Helper.getEnums(tree);
+        ContextAnalysis ctxAnal = new ContextAnalysis(funcs, structs, enums);
         
         Exception e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
         assertEquals("Error in line 1:41 Variable with name \"x\" has not been initialized.", e.getMessage());

src/test/java/VoidTest.java

@@ -0,0 +1,101 @@
+import de.hsrm.compiler.Klang.ContextAnalysis;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class VoidTest {
+
+    @Test
+    void shouldNotThrowIfVoidIsUsedAsReturnType() {
+        // given
+        var tree = Helper.prepareParser("function foo(): void { let a: int = 0; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfVoidFunctionIsCalled() {
+        // given
+        var tree = Helper.prepareParser("""
+                function foo(): void {
+                    let a: int = 0;
+                }
+                function bar(): int {
+                    foo();
+                    return 1;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldThrowIfVoidFunctionIsAssignedToVariable() {
+        // given
+        var tree = Helper.prepareParser("""
+                function foo(): void {
+                    let a: int = 0;
+                }
+                function bar(): int {
+                    let a: int = foo();
+                    return 1;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 5:4 Type mismatch: cannot combine int and void", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowIfValueIsReturnedFromVoidFunction() {
+        // given
+        var tree = Helper.prepareParser("function foo(): void { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:23 Cannot return an expression from a void function.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowIfVoidIsUsedAsParameterType() {
+        // given
+        var tree = Helper.prepareParser("function foo(a: void): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:13 Type void cannot be used to declare a parameter.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowIfVoidIsUsedAsVariableType() {
+        // given
+        var tree = Helper.prepareParser("function foo(): int { let a: void; return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:22 Type void can not be used to declare variables.", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowIfVoidIsUsedAsStructFieldType() {
+        // given
+        var tree = Helper.prepareParser("struct bar { a: void; } function foo(): int { return 1; } foo();");
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
+        assertEquals("Error in line 1:13 Type void can not be used as a struct field type.", e.getMessage());
+    }
+
+}

src/test/struct/struct.c

@@ -94,6 +94,11 @@ int testStructCreation() {
   struct_testExpected_l("init inner field a", 20, resultRec->b->a);
   struct_testExpected_s("init inner field b", NULL, resultRec->b->b);
 
+  // The result of this test is always 1 because if the tests fail
+  // a segmentation fault occurs.
+  long alignmentResult = isStackAlignedBeforeFunctionCall();
+  struct_testExpected_l("stack alignment before malloc", 1, alignmentResult);
+
   free(resultRec);
   free(innerStruct);
 }