Merge pull request 'feature/char-support' (#3) from feature/char-support into master

Reviewed-on: #3

.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/compiler.xml

@@ -10,7 +10,7 @@
       </profile>
     </annotationProcessing>
     <bytecodeTargetLevel>
-      <module name="klang" target="11" />
+      <module name="klang" target="17" />
     </bytecodeTargetLevel>
   </component>
 </project>

klang.iml

@@ -1,6 +1,6 @@
 <?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_11">
+  <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://$MODULE_DIR$">

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

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

@@ -33,7 +33,7 @@ parameter
   ;
 
 braced_block
-  : OBRK statement+ CBRK
+  : OBRK (statement | functionCall SCOL)+ CBRK
   ;
 
 
@@ -73,7 +73,7 @@ field_assignment
   ;
 
 return_statement
-  : RETURN expression SCOL
+  : RETURN expression? SCOL
   ;
 
 destroy_statement
@@ -107,6 +107,7 @@ atom
   : INTEGER_LITERAL #intAtom
   | BOOLEAN_LITERAL #boolAtom
   | FLOAT_LITERAL #floatAtom
+  | CHAR_LITERAL #charAtom
   | NULL # nullAtom
   | IDENT #variable
   ;
@@ -119,7 +120,9 @@ type
   : INTEGER
   | BOOLEAN
   | FLOAT
+  | CHAR
   | IDENT
+  | VOID
   ;
 
 functionCall
@@ -183,9 +186,13 @@ SUB: '-';
 MOD: '%';
 DIV: '/';
 
+SQUOT: '\'';
+
 BOOLEAN: 'bool';
 INTEGER: 'int';
 FLOAT: 'float';
+CHAR: 'char';
+VOID: 'void';
 
 INTEGER_LITERAL
   : [0-9]+
@@ -200,6 +207,10 @@ BOOLEAN_LITERAL
   | 'false'
   ;
 
+CHAR_LITERAL
+  : SQUOT [ -~] SQUOT
+  ;
+
 IDENT
   : [a-zA-Z][a-zA-Z0-9]*
   ;

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

@@ -8,10 +8,12 @@ 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, FunctionDefinition> functionDefs;
   Map<String, StructDefinition> structDefs;
@@ -66,25 +68,32 @@ 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 statementsOrFunctionCalls = new ArrayList<Node>();
+    var hasReturn = false;
 
-    for (int i = 0; i < declaredStatementCount; i++) {
-      Node currentStatement = this.visit(ctx.statement(i));
-      statements[i] = (Statement) currentStatement;
-      actualStatementCount += 1;
+    for (var child: ctx.children) {
+      var statementOrFunctionCall = visit(child);
 
-      // 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)) {
+      // The children array contains more than just the statements or function calls
+      // but everything else evaluates to null, so we can skip it.
+      if (statementOrFunctionCall == null) {
+        continue;
+      }
+
+      statementsOrFunctionCalls.add(statementOrFunctionCall);
+
+      if (
+          statementOrFunctionCall.type != null
+          && !(statementOrFunctionCall instanceof VariableDeclaration)
+          && !statementOrFunctionCall.type.equals(Type.getVoidType())
+      ) {
         // check whether the type matches
         try {
-          this.currentDeclaredReturnType.combine(currentStatement.type);
+          currentDeclaredReturnType.combine(statementOrFunctionCall.type);
         } catch (Exception e) {
-          throw new RuntimeException(
-              Helper.getErrorPrefix(currentStatement.line, currentStatement.col) + e.getMessage());
+          var line = statementOrFunctionCall.line;
+          var col = statementOrFunctionCall.col;
+          throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
         }
 
         // since we have a return guaranteed, every statement
@@ -94,19 +103,12 @@ 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];
-      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(statementsOrFunctionCalls.toArray(new Node[0]));
+
     if (hasReturn) {
-      result.type = this.currentDeclaredReturnType;
+      result.type = currentDeclaredReturnType;
     }
 
     result.line = ctx.start.getLine();
@@ -184,6 +186,11 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     var line = ctx.start.getLine();
     var col = ctx.start.getCharPositionInLine();
 
+    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 (!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);
@@ -199,8 +206,8 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    if (vars.get(variableName) != null) {
-      var error = "Redeclaration of variable with name \"" + variableName + "\".";
+    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);
     }
 
@@ -236,31 +243,27 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @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;
@@ -268,66 +271,55 @@ 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.structDefs, 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;
@@ -338,23 +330,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     var baseName = ctx.IDENT(0).getText();
     var line = ctx.start.getLine();
     var col = ctx.start.getCharPositionInLine();
-
-    // Create a list of member names. This excludes
-    // the first entry as it is the base name.
-    var path = new ArrayList<String>();
-    for (int i = 1; i < ctx.IDENT().size(); i++) {
-      path.add(ctx.IDENT(i).getText());
-    }
+    var path = createStructPath(ctx.IDENT());
 
     // Determine if the base name points to an enum or a variable
     var enumDef = enumDefs.get(baseName);
     if (enumDef != null) {
-      if (path.size() != 1) {
+      if (path.length != 1) {
         var error = "Illegal access to enum " + enumDef.name + ".";
         throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
       }
 
-      var enumValueName = path.get(0);
+      var enumValueName = path[0];
       var enumValue = Arrays.stream(enumDef.enums)
               .filter(e -> e.value.equals(enumValueName))
               .findFirst()
@@ -371,29 +357,11 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
       return enumAccessExpression;
     }
 
-    // Get the referenced variable, make sure it is defined
-    var variableDef = vars.get(baseName);
-    if (variableDef == null) {
-      var error = "Variable with name " + baseName + " 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()) {
-      var 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
-    var structName = variableDef.type.getName();
-    Type resultType;
-    try {
-      resultType = Helper.drillType(structDefs, structName, path.toArray(new String[0]), 0);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
-    }
-
-    var memberAccessExpression = new MemberAccessExpression(baseName, structName, path.toArray(new String[0]));
+    var memberAccessExpression = new MemberAccessExpression(baseName, variableOrParameter.type.getName(), path);
     memberAccessExpression.type = resultType;
     memberAccessExpression.line = line;
     memberAccessExpression.col = col;
@@ -459,18 +427,21 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitEqualityExpression(KlangParser.EqualityExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
+    // Since there are countless combinations of types that are comparable
+    // to each other we use Type::combine to figure out if two types
+    // may be compared to each other
     try {
       lhs.type.combine(rhs.type);
     } catch (Exception e) {
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
     }
 
-    EqualityExpression result = new EqualityExpression((Expression) lhs, (Expression) rhs);
+    var result = new EqualityExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -479,18 +450,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitNotEqualityExpression(KlangParser.NotEqualityExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    try {
-      lhs.type.combine(rhs.type);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
+    if (!lhs.type.isPrimitiveType() || !rhs.type.isPrimitiveType()) {
+      var error = "Can only compare primitives.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    NotEqualityExpression result = new NotEqualityExpression((Expression) lhs, (Expression) rhs);
+    var result = new NotEqualityExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -499,20 +469,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitLessThanExpression(KlangParser.LessThanExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    try {
-      lhs.type.combine(rhs.type);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
+    if (!lhs.type.isPrimitiveType() || !rhs.type.isPrimitiveType()) {
+      var error = "Can only compare primitives.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    checkNumeric(lhs, rhs, line, col);
-
-    LTExpression result = new LTExpression((Expression) lhs, (Expression) rhs);
+    var result = new LTExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -521,23 +488,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitGreaterThanExpression(KlangParser.GreaterThanExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    try {
-      lhs.type.combine(rhs.type);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
-    }
-
-    if (!lhs.type.isNumericType() || !rhs.type.isNumericType()) {
-      String error = "Only numeric types are allowed for this expression.";
+    if (!lhs.type.isPrimitiveType() || !rhs.type.isPrimitiveType()) {
+      var error = "Can only compare primitives.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    GTExpression result = new GTExpression((Expression) lhs, (Expression) rhs);
+    var result = new GTExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -546,20 +507,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitLessThanOrEqualToExpression(KlangParser.LessThanOrEqualToExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    try {
-      lhs.type.combine(rhs.type);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
+    if (!lhs.type.isPrimitiveType() || !rhs.type.isPrimitiveType()) {
+      var error = "Can only compare primitives.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    checkNumeric(lhs, rhs, line, col);
-
-    LTEExpression result = new LTEExpression((Expression) lhs, (Expression) rhs);
+    var result = new LTEExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -568,20 +526,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
 
   @Override
   public Node visitGreaterThanOrEqualToExpression(KlangParser.GreaterThanOrEqualToExpressionContext ctx) {
-    Node lhs = this.visit(ctx.lhs);
-    Node rhs = this.visit(ctx.rhs);
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+    var lhs = visit(ctx.lhs);
+    var rhs = visit(ctx.rhs);
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    try {
-      lhs.type.combine(rhs.type);
-    } catch (Exception e) {
-      throw new RuntimeException(Helper.getErrorPrefix(line, col) + e.getMessage());
+    if (!lhs.type.isPrimitiveType() || !rhs.type.isPrimitiveType()) {
+      var error = "Can only compare primitives.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
-    checkNumeric(lhs, rhs, line, col);
-
-    GTEExpression result = new GTEExpression((Expression) lhs, (Expression) rhs);
+    var result = new GTEExpression((Expression) lhs, (Expression) rhs);
     result.type = Type.getBooleanType();
     result.line = line;
     result.col = col;
@@ -603,7 +558,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     }
 
     checkNumeric(lhs, rhs, line, col);
-    
+
     result.line = line;
     result.col = col;
     return result;
@@ -637,7 +592,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     int line = ctx.start.getLine();
     int col = ctx.start.getCharPositionInLine();
     DivisionExpression result = new DivisionExpression((Expression) lhs, (Expression) rhs);
-    
+
     try {
       result.type = lhs.type.combine(rhs.type);
     } catch (Exception e) {
@@ -645,7 +600,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     }
 
     checkNumeric(lhs, rhs, line, col);
-    
+
     result.line = line;
     result.col = col;
     return result;
@@ -671,7 +626,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
       String error = "Only integers are allowed for modulo.";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
-    
+
     result.line = line;
     result.col = col;
     return result;
@@ -684,7 +639,7 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     result.type = expression.type;
     result.line = ctx.start.getLine();
     result.col = ctx.start.getCharPositionInLine();
-    
+
     if (!result.type.isNumericType()) {
       String error = "Only numeric types are allowed for this expression.";
       throw new RuntimeException(Helper.getErrorPrefix(result.line, result.col) + error);
@@ -711,24 +666,20 @@ 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;
@@ -766,6 +717,17 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     return n;
   }
 
+  @Override
+  public Node visitCharAtom(KlangParser.CharAtomContext ctx) {
+    // I had no idea how to design the grammar so that the quotes
+    // are separate from the char, so I cheat here...
+    var n = new CharExpression(ctx.CHAR_LITERAL().getText().charAt(1));
+    n.type = Type.getCharType();
+    n.line = ctx.start.getLine();
+    n.col = ctx.start.getCharPositionInLine();
+    return n;
+  }
+
   @Override
   public Node visitNullAtom(KlangParser.NullAtomContext ctx) {
     Node n = new NullExpression();
@@ -802,6 +764,11 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     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);
+    }
+
     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);
@@ -832,42 +799,43 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
     currentDeclaredReturnType = returnType;
     currentFunctionDefinitionName = name;
 
-    if (!returnType.isPrimitiveType() && !structDefs.containsKey(returnType.getName()) && !enumDefs.containsKey(returnType.getName())) {
+    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 of the current function
+    // 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<>();
+
 
-    // Process the parameter list by visiting every parameter in it
     var paramCount = ctx.params.parameter().size();
-    var params = new Parameter[paramCount];
+    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
-      var param = (Parameter) visit(ctx.params.parameter(i));
-      params[i] = param;
+      functionParameters[i] = (Parameter) visit(ctx.params.parameter(i));
 
-      // add the param as a variable
-      var var = new VariableDeclaration(param.name);
-      var.initialized = true; // parameters can always be considered initialized
-      var.type = param.type;
-      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
     var block = visit(ctx.braced_block());
-    if (block.type == null) {
+    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);
     }
 
-    var functionDef = new FunctionDefinition(name, params, (Block) block);
+    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();
@@ -879,26 +847,29 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
   public Node visitParameter(KlangParser.ParameterContext ctx) {
     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 (parameterType.equals(Type.getVoidType())) {
+      var error = "Type " + parameterType.getName() + " cannot be used to declare a parameter.";
+      throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
+    }
 
     if (structDefs.containsKey(parameterName)) {
-      var line = ctx.start.getLine();
-      var col = ctx.start.getCharPositionInLine();
       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 line = ctx.start.getLine();
-      var col = ctx.start.getCharPositionInLine();
       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 line = ctx.type_annotation().start.getLine();
-      var col = ctx.type_annotation().start.getCharPositionInLine();
+      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(line, col) + error);
+      throw new RuntimeException(Helper.getErrorPrefix(typeLine, typeCol) + error);
     }
 
     var parameter = new Parameter(parameterName);
@@ -910,55 +881,60 @@ public class ContextAnalysis extends KlangBaseVisitor<Node> {
   }
 
   @Override
-  public Node visitFunctionCallExpression(KlangParser.FunctionCallExpressionContext ctx) {
-    String name = ctx.functionCall().IDENT().getText();
-    int line = ctx.start.getLine();
-    int col = ctx.start.getCharPositionInLine();
+  public Node visitFunctionCall(KlangParser.FunctionCallContext ctx) {
+    var name = ctx.IDENT().getText();
+    var line = ctx.start.getLine();
+    var col = ctx.start.getCharPositionInLine();
 
-    var functionDef = this.functionDefs.get(name);
+    var functionDef = functionDefs.get(name);
     if (functionDef == null) {
-      String error = "Function with name \"" + name + "\" not defined.";
+      var 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 = functionDef.parameters.length;
+    var argCount = ctx.arguments().expression().size();
+    var paramCount = functionDef.parameters.length;
     if (argCount != paramCount) {
-      String error = "Function \"" + name + "\" expects " + paramCount + " parameters, but got " + argCount + ".";
+      var error = "Function \"" + name + "\" expects " + paramCount + " parameters, but got " + argCount + ".";
       throw new RuntimeException(Helper.getErrorPrefix(line, col) + error);
     }
 
     // Evaluate every argument
-    Expression[] args = new Expression[argCount];
+    var args = new Expression[argCount];
     for (int i = 0; i < argCount; i++) {
-      Expression expression = (Expression) this.visit(ctx.functionCall().arguments().expression(i));
+      var expression = (Expression) visit(ctx.arguments().expression(i));
       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);
+    var result = new FunctionCall(name, args);
     result.type = functionDef.type;
     result.line = line;
     result.col = col;
     return result;
   }
 
+  @Override
+  public Node visitFunctionCallExpression(KlangParser.FunctionCallExpressionContext ctx) {
+    return visit(ctx.functionCall());
+  }
+
   @Override
   public Node visitConstructorCallExpression(KlangParser.ConstructorCallExpressionContext ctx) {
     String name = ctx.IDENT().getText();
     int line = ctx.start.getLine();
     int col = ctx.start.getCharPositionInLine();
-    
+
     // Get the corresponding struct definition
     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);
     }
-    
+
     // Make sure the number of arguments match the number of struct fields
     int fieldCount = struct.fields.length;
     int argCount = ctx.arguments().expression().size();
@@ -988,19 +964,52 @@ 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

@@ -210,7 +210,7 @@ public class GetDefinitions extends KlangBaseVisitor<Node> {
             parameters.put(paramName, parameter);
         }
 
-        var functionDef = new FunctionDefinition(funcName, parameters.values().toArray(new Parameter[0]), null);
+        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;

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

@@ -1,9 +1,11 @@
 package de.hsrm.compiler.Klang;
 
+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.types.Type;
 import de.hsrm.compiler.Klang.visitors.EvalVisitor;
 import de.hsrm.compiler.Klang.visitors.GenASM;
 import de.hsrm.compiler.Klang.visitors.PrettyPrintVisitor;
@@ -120,7 +122,11 @@ public class Klang {
       System.out.println("\nEvaluating the source code:");
       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;
     }
 

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

@@ -4,8 +4,8 @@ import de.hsrm.compiler.Klang.types.Type;
 import java.util.Map;
 
 public class Value {
+    private final Object value;
     public Type type;
-    private Object value;
 
     public Value(Object value) {
         this.value = value;
@@ -17,19 +17,23 @@ public class Value {
     }
 
     public Object asObject() {
-        return this.value;
+        return value;
     }
 
     public int asInteger() {
-        return (int) this.value;
+        return (int) value;
     }
     
     public double asFloat() {
-        return (double) this.value;
+        return (double) value;
     }
 
     public boolean asBoolean() {
-        return (boolean) this.value;
+        return (boolean) value;
+    }
+
+    public char asChar() {
+        return (char) value;
     }
 
     @SuppressWarnings("unchecked")

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

@@ -172,6 +172,10 @@ public class ASM {
     mnemonics.add(new Cqto());
   }
 
+  public void leave() {
+    mnemonics.add(new Leave());
+  }
+
   public void ret() {
     mnemonics.add(new Ret());
   }

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/nodes/Block.java

@@ -1,14 +1,13 @@
 package de.hsrm.compiler.Klang.nodes;
 
-import de.hsrm.compiler.Klang.nodes.statements.Statement;
 import de.hsrm.compiler.Klang.visitors.Visitor;
 
 public class Block extends Node {
 
-    public Statement[] statements;
+    public Node[] statementsOrFunctionCalls;
 
-    public Block(Statement[] statements) {
-        this.statements = statements;
+    public Block(Node[] statements) {
+        this.statementsOrFunctionCalls = statements;
     }
 
     @Override

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/expressions/CharExpression.java

@@ -0,0 +1,16 @@
+package de.hsrm.compiler.Klang.nodes.expressions;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class CharExpression extends Expression {
+    public char c;
+
+    public CharExpression(char c) {
+        this.c = c;
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}

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

@@ -32,7 +32,7 @@ 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

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

@@ -0,0 +1,47 @@
+package de.hsrm.compiler.Klang.types;
+
+import de.hsrm.compiler.Klang.Value;
+
+public class CharType extends PrimitiveType {
+    private static CharType instance = null;
+
+    public static CharType getType() {
+        if (instance != null) {
+            return instance;
+        }
+        instance = new CharType();
+        return instance;
+    }
+
+    @Override
+    public String getName() {
+        return "char";
+    }
+
+    @Override
+    public Type combine(Type that) {
+        if (this.equals(that)) {
+            return this;
+        }
+
+        if (that.equals(Type.getIntegerType())) {
+            return this;
+        }
+
+        throw new RuntimeException("Type mismatch: cannot combine " + getName() + " and " + that.getName());
+    }
+
+    @Override
+    public boolean valuesEqual(Value a, Value b) {
+        return ((int) a.asChar()) == ((int) b.asChar());
+    }
+
+    @Override
+    public boolean equals(Object that) {
+        if (this == that) {
+            return true;
+        }
+
+        return that instanceof CharType;
+    }
+}

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

@@ -36,7 +36,7 @@ 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

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

@@ -35,8 +35,12 @@ public class IntegerType extends NumericType {
       return Type.getFloatType();
     }
 
+    if (that.equals(Type.getCharType())) {
+      return Type.getCharType();
+    }
+
     // 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

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

@@ -1,11 +1,6 @@
 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 class NamedType extends Type {
     public String name;
@@ -21,7 +16,7 @@ public class NamedType extends Type {
 
     @Override
     public Type combine(Type that) {
-        if(this.equals(that)) {
+        if(this.equals(that) || (that instanceof NullType)) {
             return this;
         }
 
@@ -49,8 +44,7 @@ public class NamedType extends Type {
             return true;
         }
 
-        if (that instanceof NamedType) {
-            var thatType = (NamedType) that;
+        if (that instanceof NamedType thatType) {
             return getName().equals(thatType.getName());
         }
 

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

@@ -23,7 +23,7 @@ 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

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

@@ -23,16 +23,26 @@ public abstract class Type {
     return FloatType.getType();
   }
 
+  public static CharType getCharType() {
+    return CharType.getType();
+  }
+
   public static NullType getNullType() {
     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 "char": return getCharType();
       case "null": return getNullType();
+      case "void": return getVoidType();
       default: return new NamedType(name);
     }
   }
@@ -42,4 +52,4 @@ public abstract class Type {
   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

@@ -10,6 +10,7 @@ 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.NullType;
 import de.hsrm.compiler.Klang.types.Type;
 
 public class EvalVisitor implements Visitor<Value> {
@@ -44,6 +45,11 @@ public class EvalVisitor implements Visitor<Value> {
     return result;
   }
 
+  @Override
+  public Value visit(CharExpression e) {
+    return new Value(e.c, Type.getCharType());
+  }
+
   @Override
   public Value visit(EqualityExpression e) {
     var lhs = e.lhs.welcome(this);
@@ -394,13 +400,16 @@ 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);
+    for (var stmt : e.statementsOrFunctionCalls) {
+      var result = stmt.welcome(this);
       if (result != null) {
         return result;
       }
@@ -428,7 +437,7 @@ 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;
@@ -502,12 +511,17 @@ 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/GenASM.java

@@ -13,16 +13,16 @@ import de.hsrm.compiler.Klang.types.Type;
 import java.util.*;
 
 public class GenASM implements Visitor<Void> {
-  private class FloatWriter {
-    private StringBuilder sb = new StringBuilder();
+  private static class FloatWriter {
+    private final StringBuilder sb = new StringBuilder();
     private int id = -1;
 
     public String getFloat(double d) {
-      Long longBits = Double.doubleToRawLongBits(d);
-      String binary = Long.toBinaryString(longBits);
+      long longBits = Double.doubleToRawLongBits(d);
+      StringBuilder binary = new StringBuilder(Long.toBinaryString(longBits));
       int padCount = 64 - binary.length();
       while (padCount > 0) {
-        binary = "0" + binary;
+        binary.insert(0, "0");
         padCount--;
       }
       String upper = binary.substring(0, 32);
@@ -59,49 +59,19 @@ public class GenASM implements Visitor<Void> {
     }
   }
 
-  private ASM asm;
-  private FloatWriter fw = new FloatWriter();
-  private String mainName;
+  private final ASM asm;
+  private final FloatWriter fw = new FloatWriter();
+  private final String mainName;
+
   Map<String, Integer> env = new HashMap<>();
   Map<String, StructDefinition> structs;
-  Set<String> vars;
   String[] registers = { "%rdi", "%rsi", "%rdx", "%rcx", "%r8", "%r9" };
   String[] floatRegisters = { "%xmm0", "%xmm1", "%xmm2", "%xmm3", "%xmm4", "%xmm5", "%xmm6", "%xmm7" };
-  private int lCount = 0; // Invariant: lCount is used
-  private int currentFunctionStartLabel = 0;
-  private Parameter[] currentFunctionParams;
 
-  private boolean prepareRegisters(Expression lhs, Expression rhs) {
-    boolean lhsIsFloat = lhs.type.equals(Type.getFloatType());
-    boolean rhsIsFloat = rhs.type.equals(Type.getFloatType());
-    if (lhsIsFloat && rhsIsFloat) {
-      lhs.welcome(this);
-      asm.mov("sd", "%xmm0", "%xmm2");
-      rhs.welcome(this);
-      asm.mov("sd", "%xmm2", "%xmm0");
-      asm.mov("sd", "%xmm2", "%xmm0");
-      return true;
-    } else if (lhsIsFloat && !rhsIsFloat) {
-      lhs.welcome(this);
-      rhs.welcome(this);
-      asm.cvtsi2sd("%rax", "%xmm1");
-      return true;
-    } else if (!lhsIsFloat && rhsIsFloat) {
-      lhs.welcome(this);
-      asm.cvtsi2sd("%rax", "%xmm2");
-      rhs.welcome(this);
-      asm.mov("sd", "%xmm0", "%xmm1");
-      asm.mov("sd", "%xmm2", "%xmm0");
-      return true;
-    } else {
-      lhs.welcome(this);
-      asm.push("q", "%rax");
-      rhs.welcome(this);
-      asm.mov("q", "%rax", "%rbx");
-      asm.pop("q", "%rax");
-      return false;
-    }
-  }
+  private int lCount = 0;
+  private int currentFunctionStartLabel = 0;
+  private long bytesToClearFromTheStack = 0;
+  private FunctionDefinition currentFunctionDef;
 
   public GenASM(String mainName, Map<String, StructDefinition> structs) {
     this.mainName = mainName;
@@ -109,10 +79,6 @@ public class GenASM implements Visitor<Void> {
     this.asm = new ASM();
   }
 
-  public GenASM(Map<String, StructDefinition> structs) {
-    this("main", structs);
-  }
-
   public String toAsm() {
     return asm.toAsm();
   }
@@ -136,6 +102,12 @@ public class GenASM implements Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visit(CharExpression e) {
+    asm.mov("q", "$" + ((int) e.c), "%rax");
+    return null;
+  }
+
   @Override
   public Void visit(Variable e) {
     if (e.type.equals(Type.getFloatType())) {
@@ -326,10 +298,19 @@ public class GenASM implements Visitor<Void> {
   @Override
   public Void visit(ModuloExpression e) {
     e.lhs.welcome(this);
+
+    // A single pushq brings the stack out of 16 byte alignment,
+    // so we need to increase the stack by another 8 bytes
+    asm.sub("q", "$8", "%rsp");
+
     asm.push("q", "%rax");
     e.rhs.welcome(this);
     asm.mov("q", "%rax", "%rbx");
     asm.pop("q", "%rax");
+
+    // Which we remove afterwards
+    asm.add("q", "$8", "%rsp");
+
     asm.cqto();
     asm.idiv("q", "%rbx");
     asm.mov("q", "%rdx", "%rax");
@@ -357,7 +338,7 @@ public class GenASM implements Visitor<Void> {
 
     // Werte LHS aus
     // Wenn LHS != 0 bedeutet das true
-    // also können wir direkt sagen dass das Ergebnis true ist
+    // also können wir direkt sagen, dass das Ergebnis true ist
     e.lhs.welcome(this);
     asm.cmp("q", 0, "%rax");
     asm.jne(lblTrue);
@@ -375,11 +356,11 @@ public class GenASM implements Visitor<Void> {
     asm.mov("q", 1, "%rax");
     asm.jmp(lblEnd);
 
-    // Die Expressoin wertet zu false aus
+    // Die Expression wertet zu false aus
     asm.label(lblFalse);
     asm.mov("q", 0, "%rax");
 
-    // Das hier ist das ende
+    // Das hier ist das Ende
     asm.label(lblEnd);
     return null;
   }
@@ -392,7 +373,7 @@ public class GenASM implements Visitor<Void> {
 
     // Werte LHS aus
     // Wenn LHS == 0, bedeutet das false
-    // also können wir direkt sagen dass das Ergebnis false ist
+    // also können wir direkt sagen, dass das Ergebnis false ist
     e.lhs.welcome(this);
     asm.cmp("q", 0, "%rax");
     asm.je(lblFalse);
@@ -410,11 +391,11 @@ public class GenASM implements Visitor<Void> {
     asm.mov("q", 1, "%rax");
     asm.jmp(lblEnd);
 
-    // Die Expressoin wertet zu false aus
+    // Die Expression wertet zu false aus
     asm.label(lblFalse);
     asm.mov("q", 0, "%rax");
 
-    // Das hier ist das ende
+    // Das hier ist das Ende
     asm.label(lblEnd);
     return null;
   }
@@ -424,9 +405,9 @@ public class GenASM implements Visitor<Void> {
     int lblFalse = ++lCount;
     int lblEnd = ++lCount;
 
-    // Werte LHS aus
-    // Wenn LHS != 0 bedeutet das true, also jumpe zum false Teil
-    // Wenn nicht, falle durch zum true Teil
+    // Werte LHS aus.
+    // Wenn LHS != 0 bedeutet das true, also springe zum false Teil.
+    // Wenn nicht, falle durch zum true Teil.
     e.lhs.welcome(this);
     asm.cmp("q", 0, "%rax");
     asm.jne(lblFalse);
@@ -550,18 +531,41 @@ public class GenASM implements Visitor<Void> {
 
   @Override
   public Void visit(ReturnStatement e) {
-    e.expression.welcome(this);
-    asm.mov("q", "%rbp", "%rsp");
-    asm.pop("q", "%rbp");
+    if (e.expression != null) {
+      e.expression.welcome(this);
+    }
+
+    // The ReturnStatement visitor is kindly removing the
+    // stack space that was allocated by the FunctionDefinition
+    // before executing the function body.
+    if (bytesToClearFromTheStack > 0) {
+      asm.add("q", "$" + bytesToClearFromTheStack, "%rsp");
+    }
+
+    asm.leave();
     asm.ret();
     return null;
   }
 
   @Override
   public Void visit(Block e) {
-    for (var statement : e.statements) {
-      statement.welcome(this);
+    for (var statementOrFunctionCall : e.statementsOrFunctionCalls) {
+      statementOrFunctionCall.welcome(this);
     }
+
+    // It's possible (and allowed -> void functions) that there is no return statement
+    // in the outermost block of a function body. In this case, no
+    // direct descendant of Block will be a return statement.
+    // This means we have to generate an implicit return, otherwise
+    // the code would fall through to the next function below :D
+    // We also have to clean up the stack which is the ReturnStatement's job.
+
+    // Check if we have to generate an implicit return
+    var lastStatementOrFunctionCall = e.statementsOrFunctionCalls[e.statementsOrFunctionCalls.length - 1];
+    if (currentFunctionDef.block == e && !(lastStatementOrFunctionCall instanceof ReturnStatement)) {
+      visit(new ReturnStatement());
+    }
+
     return null;
   }
 
@@ -574,32 +578,29 @@ public class GenASM implements Visitor<Void> {
       e.name = "main_by_user";
     }
 
-    int lblStart = ++lCount;
-    this.currentFunctionStartLabel = lblStart;
-    this.currentFunctionParams = e.parameters;
+    // Remember the current function definition so everyone below us knows where they belong to.
+    currentFunctionDef = e;
+
+    var lblStart = ++lCount;
+    currentFunctionStartLabel = lblStart;
     asm.functionHead(e.name);
     asm.push("q", "%rbp");
     asm.mov("q", "%rsp", "%rbp");
     asm.label(lblStart);
 
-    // hole die anzahl der lokalen variablen
-    this.vars = new TreeSet<String>();
-    HashMap<String, Type> types = new HashMap<String, Type>();
-    GetVars getvars = new GetVars(vars, types);
-    getvars.visit(e);
+    // Create a new environment
+    env = new HashMap<>();
 
-    // Erzeuge ein environment
-    this.env = new HashMap<String, Integer>();
+    // Remember the offsets of the arguments that were placed on the stack.
+    var offset = 16; // Variables that were passed via the stack are located above our BSP
+    var ri = 0;
+    var fi = 0;
 
-    // Merke dir die offsets der parameter, die direkt auf den stack gelegt wurden
-    int offset = 16; // Per Stack übergebene Parameter liegen über unserem BSP
-    int ri = 0;
-    int fi = 0;
-    // Per stack übergebene variablen in env registrieren
+    // Add arguments that were passed via the stack to the environment
     var registerParameters = new ArrayList<Parameter>();
     for (int i = 0; i < e.parameters.length; i++) {
       if (e.parameters[i].type.equals(Type.getFloatType())) {
-        if (fi >= this.floatRegisters.length) {
+        if (fi >= floatRegisters.length) {
           // parameter is on stack already
           env.put(e.parameters[i].name, offset);
           offset += 8;
@@ -609,7 +610,7 @@ public class GenASM implements Visitor<Void> {
           fi++;
         }
       } else {
-        if (ri >= this.registers.length) {
+        if (ri >= registers.length) {
           // parameter is on stack already
           env.put(e.parameters[i].name, offset);
           offset += 8;
@@ -624,29 +625,58 @@ public class GenASM implements Visitor<Void> {
     offset = 0;
     ri = 0;
     fi = 0;
+
+    // Push arguments that were passed via registers onto the stack
+    // and add them to the environment.
     for (var param: registerParameters) {
       if (param.type.equals(Type.getFloatType())) {
-        asm.mov("q", this.floatRegisters[fi], "%rax");
+        asm.mov("q", floatRegisters[fi], "%rax");
         asm.push("q", "%rax");
         offset -= 8;
-        this.env.put(param.name, offset); // negative, liegt unter aktuellem BP
+        env.put(param.name, offset); // negative, liegt unter aktuellem BP
         fi++;
       } else {
-        asm.push("q", this.registers[ri]);
+        asm.push("q", registers[ri]);
         offset -= 8;
-        this.env.put(param.name, offset); // negative, liegt unter aktuellem BP
+        env.put(param.name, offset); // negative, liegt unter aktuellem BP
         ri++;
       }
     }
 
-    // Reserviere Platz auf dem Stack für jede lokale variable
-    for (String lok_var : vars) {
-      offset -= 8;
-      asm.push("q", 0);
-      this.env.put(lok_var, offset);
+    // Reserve memory on the stack for the local variables.
+    if (e.localVariables.length > 0) {
+      // Each variable is at most 8 bytes in size.
+      asm.sub("q", "$" + (8 * e.localVariables.length), "%rsp");
+
+      // Save the offsets (they are relative to rbp)
+      for (var localVariable : e.localVariables) {
+        offset -= 8;
+        env.put(localVariable.name, offset);
+      }
     }
 
+    // Check the stack alignment and correct if necessary
+    // The padding needs to happen after the register parameters
+    // and local variables were pushed to the stack because otherwise
+    // the relative offsets to rbp will be wrong.
+    if ((registerParameters.size() + e.localVariables.length) % 2 != 0) {
+      // Since each variable is 8 bytes and the stack is 16 byte aligned
+      // we need to add 8 bytes to the stack to make it aligned
+      // if there is an odd number of parameters and local variables.
+      asm.sub("q", "$8", "%rsp");
+    }
+
+    // I need to clear the stack here so that the top most element is the old rbp that
+    // ret uses to return to the caller but code that gets generated after visiting the
+    // function body will never be reached since the block node is guaranteed to
+    // contain a return node that results in a ret command being executed before this
+    // code would be reached. As a workaround (and a dirty, dirty hack) I indicate
+    // to the return node visitor how many bytes need to be cleared from the stack.
+    var wasStackPadded = (registerParameters.size() + e.localVariables.length) % 2 != 0;
+    bytesToClearFromTheStack = 8L * (registerParameters.size() + e.localVariables.length + (wasStackPadded ? 1 : 0));
+
     e.block.welcome(this);
+
     return null;
   }
 
@@ -665,15 +695,18 @@ public class GenASM implements Visitor<Void> {
         asm.push("q", "%rax");
       }
 
-      // push args into local var locations, last arg is ontop of the stack
+      // push args into local var locations, last arg is on top of the stack
       for (int i = e.arguments.length - 1; i >= 0; i--) {
-        asm.pop("q", this.env.get(this.currentFunctionParams[i].name) + "(%rbp)");
+        asm.pop("q", env.get(currentFunctionDef.parameters[i].name) + "(%rbp)");
       }
 
-      asm.jmp(this.currentFunctionStartLabel);
+      asm.jmp(currentFunctionStartLabel);
       return null;
     }
 
+    // This holds the indices into the arguments array for
+    // arguments that need to be passed to the callee via the stack
+    var stackIndices = new ArrayList<Integer>();
 
     if (e.arguments.length > 0) {
       // Mapping arguments index -> xmm registers index
@@ -684,9 +717,6 @@ public class GenASM implements Visitor<Void> {
       int[] rIdxs = new int[this.registers.length];
       int ri = -1;
 
-      // Mapping arguments index -> stack
-      ArrayList<Integer> stackIdxs = new ArrayList<Integer>();
-
       // Go through arguments
       // sort them into the memory regions they go when being passed to functions
       for (int i = 0; i < e.arguments.length; i++) {
@@ -698,7 +728,7 @@ public class GenASM implements Visitor<Void> {
             xmmIdxs[fi] = i;
           } else {
             // Float onto stack
-            stackIdxs.add(i);
+            stackIndices.add(i);
           }
         } else {
           if (ri < this.registers.length - 1) {
@@ -707,14 +737,39 @@ public class GenASM implements Visitor<Void> {
             rIdxs[ri] = i;
           } else {
             // bool/int onto stack
-            stackIdxs.add(i);
+            stackIndices.add(i);
           }
         }
       }
 
-      // Welcome the arguments in order, push everything onto the stack
-      for (var arg : e.arguments) {
+      // Make sure that the stack is aligned after all arguments
+      // have been pushed onto the stack. Keep in mind that we
+      // may remove the top n elements from our stack so they form
+      // the base of the callee's stack.
+      if ((e.arguments.length - stackIndices.size()) % 2 != 0) {
+        asm.sub("q", "$8", "%rsp");
+      }
+
+      // Welcome the arguments in order, push everything onto the stack.
+      // We can assume that we are currently 16 byte aligned which holds
+      // true until after the result of the first argument is pushed onto
+      // the stack. After that we have to pad the stack for every argument
+      // to ensure that the stack is aligned before welcoming the argument.
+      // We get rid of the padding directly after welcome() to
+      // "tightly pack" the arguments on the stack. This way the usual
+      // 8 byte offsets are kept intact.
+      for (int i = 0; i < e.arguments.length; i++) {
+        if (i % 2 == 0) {
+          asm.sub("q", "$8", "%rsp");
+        }
+
+        var arg = e.arguments[i];
         arg.welcome(this);
+
+        if (i % 2 == 0) {
+          asm.add("q", "$8", "%rsp");
+        }
+
         if (arg.type.equals(Type.getFloatType())) {
           asm.mov("q", "%xmm0", "%rax");
           asm.push("q", "%rax");
@@ -737,22 +792,38 @@ public class GenASM implements Visitor<Void> {
         asm.mov("q", rspOffset, "%rsp", this.registers[i]);
       }
 
-      // Move everything else from a higher stack position to our stack frame start
+      // Reorder the remaining n arguments that did not fit in a register,
+      // so that the remaining n arguments occupy the last n spots on our current stack
+      // This does not manipulate the stack in any way. It just reorders it.
       int stackStartOffset = ((e.arguments.length) * 8);
-      for (int i = stackIdxs.size() - 1; i >= 0; i--) {
+      for (int i = stackIndices.size() - 1; i >= 0; i--) {
         stackStartOffset -= 8;
-        int indexInArguments = stackIdxs.get(i);
+        int indexInArguments = stackIndices.get(i);
         int rspOffset = (((e.arguments.length - indexInArguments) - 1) * 8);
         asm.mov("q", rspOffset, "%rsp", "%rax");
         asm.mov("q", "%rax", stackStartOffset, "%rsp");
       }
 
-      // Rescue RSP
-      asm.add("q", stackStartOffset, "%rsp");
+      // The top n elements of the stack prepared in the step earlier will now become
+      // the base of the callee's stack by shrinking the stack by the size of the
+      // n arguments that did not fit in registers.
+      // This must only be done if there were any arguments that did not fit in the registers.
+      if (!stackIndices.isEmpty()) {
+        asm.add("q", stackStartOffset, "%rsp");
+      }
     }
 
     // We rename a function name if it is "main"
-    asm.call(e.name.equals("main") ? "main_by_user": e.name);
+    var mainName = e.name.equals("main") ? "main_by_user": e.name;
+    asm.call(mainName);
+
+    // Remove the arguments that remained on the stack and the stack padding if there was any
+    var wasStackPadded = (e.arguments.length - stackIndices.size()) % 2 != 0;
+    var bytesToRemove = 8 * (e.arguments.length - stackIndices.size() + (wasStackPadded ? 1 : 0));
+    if (bytesToRemove > 0) {
+      asm.add("q", "$" + bytesToRemove, "%rsp");
+    }
+
     return null;
   }
 
@@ -840,10 +911,29 @@ public class GenASM implements Visitor<Void> {
 
   @Override
   public Void visit(ConstructorCall e) {
+    // Make sure the stack is aligned before calling malloc
+    if (e.args.length % 2 != 0) {
+      // an odd number of arguments means we called pushq an odd number of times
+      // which results in an unaligned stack. Subtract 8 from the stack pointer to
+      // re-align the stack
+      asm.sub("q", "$8", "%rsp");
+    }
+
     // push arguments onto the stack
-    for (var arg: e.args) {
+    for (int i = 0; i < e.args.length; i++) {
+
+      // if you want to know why this is done go and read visit(FunctionCall)
+      if (i % 2 != 0) {
+        asm.sub("q", "$8", "%rsp");
+      }
+
+      var arg = e.args[i];
       arg.welcome(this);
 
+      if (i % 2 != 0) {
+        asm.add("q", "$8", "%rsp");
+      }
+
       // move float values from xmm0 to rax first
       if (arg.type.equals(Type.getFloatType())) {
         asm.mov("q", "%xmm0", "%rax");
@@ -857,11 +947,16 @@ public class GenASM implements Visitor<Void> {
     asm.mov("l", Helper.getFieldSizeBytes(structDef), "%edi");
     asm.call("malloc@PLT");
 
-    // push args into struct memory, last arg is ontop of the stack
+    // push args into struct memory, last arg is on top of the stack
     for (int i = e.args.length - 1; i >= 0; i--) {
       asm.pop("q", Helper.getFieldOffset(structDef, i) + "(%rax)");
     }
 
+    // Get rid of the stack alignment if there was any
+    if (e.args.length % 2 != 0) {
+      asm.add("q", "$8", "%rsp");
+    }
+
     return null;
   }
 
@@ -886,7 +981,7 @@ public class GenASM implements Visitor<Void> {
 
     e.expression.welcome(this);
 
-    // Move it from xmm0 rax if its a flaot
+    // Move it from xmm0 rax if it's a float
     if (e.expression.type.equals(Type.getFloatType())) {
       asm.mov("q", "%xmm0", "%rax");
     }
@@ -904,11 +999,49 @@ public class GenASM implements Visitor<Void> {
       asm.mov("q",  Helper.getFieldOffset(structDef, e.path[i]), "%rax", "%rax");
     }
 
-    // pop the expression that is ontop of the stack into the field of the struct that has to be updated
+    // pop the expression that is on top of the stack into the field of the struct that has to be updated
     asm.pop("q", Helper.getFieldOffset(structDef, fieldNameToUpdate) + "(%rax)");
     asm.mov("q", 0 , "%rax"); // clear rax since an assignment has no result
 
     return null;
   }
 
-}
+  private boolean prepareRegisters(Expression lhs, Expression rhs) {
+    boolean lhsIsFloat = lhs.type.equals(Type.getFloatType());
+    boolean rhsIsFloat = rhs.type.equals(Type.getFloatType());
+    if (lhsIsFloat && rhsIsFloat) {
+      lhs.welcome(this);
+      asm.mov("sd", "%xmm0", "%xmm2");
+      rhs.welcome(this);
+      asm.mov("sd", "%xmm2", "%xmm0");
+      asm.mov("sd", "%xmm2", "%xmm0");
+      return true;
+    } else if (lhsIsFloat) {
+      lhs.welcome(this);
+      rhs.welcome(this);
+      asm.cvtsi2sd("%rax", "%xmm1");
+      return true;
+    } else if (rhsIsFloat) {
+      lhs.welcome(this);
+      asm.cvtsi2sd("%rax", "%xmm2");
+      rhs.welcome(this);
+      asm.mov("sd", "%xmm0", "%xmm1");
+      asm.mov("sd", "%xmm2", "%xmm0");
+      return true;
+    } else {
+      lhs.welcome(this);
+      // A single pushq brings the stack out of 16 byte alignment,
+      // so we need to increase the stack by another 8 bytes
+      asm.sub("q", "$8", "%rsp");
+
+      asm.push("q", "%rax");
+      rhs.welcome(this);
+      asm.mov("q", "%rax", "%rbx");
+      asm.pop("q", "%rax");
+
+      // Which we remove afterwards
+      asm.add("q", "$8", "%rsp");
+      return false;
+    }
+  }
+}

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

@@ -1,286 +0,0 @@
-package de.hsrm.compiler.Klang.visitors;
-
-import java.util.Map;
-import java.util.Set;
-
-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.Type;
-
-class GetVars implements Visitor<Void> {
-
-  public Set<String> vars;
-  public Map<String, Type> types;
-
-  public GetVars(Set<String> vars, Map<String, Type> types) {
-    this.vars = vars;
-    this.types = types;
-  }
-
-  @Override
-  public Void visit(IntegerExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(FloatExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(BooleanExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(Variable e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(EqualityExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(NotEqualityExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(GTExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(GTEExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(LTExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(LTEExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(AdditionExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(SubstractionExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(MultiplicationExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(DivisionExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(ModuloExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(NegateExpression e) {
-    e.lhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(OrExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(AndExpression e) {
-    e.lhs.welcome(this);
-    e.rhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(NotExpression e) {
-    e.lhs.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(IfStatement e) {
-    e.cond.welcome(this);
-    e.then.welcome(this);
-    if (e.alt != null) {
-      e.alt.welcome(this);
-    } else if (e.elif != null) {
-      e.elif.welcome(this);
-    }
-    return null;
-  }
-
-  @Override
-  public Void visit(WhileLoop e) {
-    e.cond.welcome(this);
-    e.block.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(DoWhileLoop e) {
-    e.cond.welcome(this);
-    e.block.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(ForLoop e) {
-    e.init.welcome(this);
-    e.condition.welcome(this);
-    e.step.welcome(this);
-    e.block.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(VariableDeclaration e) {
-    vars.add(e.name);
-    types.put(e.name, e.type);
-    return null;
-  }
-
-  @Override
-  public Void visit(VariableAssignment e) {
-    e.expression.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(ReturnStatement e) {
-    e.expression.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(Block e) {
-    for (var statement : e.statements) {
-      statement.welcome(this);
-    }
-    return null;
-  }
-
-  @Override
-  public Void visit(FunctionDefinition e) {
-    e.block.welcome(this);
-    return null;
-  }
-
-  @Override
-  public Void visit(FunctionCall e) {
-    for (var expression : e.arguments) {
-      expression.welcome(this);
-    }
-    return null;
-  }
-
-  @Override
-  public Void visit(Program e) {
-    e.expression.welcome(this);
-    for (var func : e.funcs) {
-      func.welcome(this);
-    }
-    return null;
-  }
-
-  @Override
-  public Void visit(Parameter e) {
-    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;
-  }
-
-  @Override
-  public Void visit(StructField e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(MemberAccessExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(EnumAccessExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(ConstructorCall e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(NullExpression e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(DestructorCall e) {
-    return null;
-  }
-
-  @Override
-  public Void visit(FieldAssignment e) {
-    return null;
-  }
-}

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

@@ -97,6 +97,14 @@ public class PrettyPrintVisitor implements Visitor<Void> {
     return null;
   }
 
+  @Override
+  public Void visit(CharExpression e) {
+    ex.write("'");
+    ex.write(e.c);
+    ex.write("'");
+    return null;
+  }
+
   @Override
   public Void visit(EqualityExpression e) {
     ex.write("(");
@@ -310,8 +318,11 @@ 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;
   }
@@ -320,7 +331,7 @@ public class PrettyPrintVisitor implements Visitor<Void> {
   public Void visit(Block e) {
     ex.write("{");
     ex.addIndent();
-    for (Statement stmt : e.statements) {
+    for (var stmt : e.statementsOrFunctionCalls) {
       ex.nl();
       stmt.welcome(this);
       if (stmt.getClass() == VariableAssignment.class || stmt.getClass() == VariableDeclaration.class) {

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

@@ -12,6 +12,7 @@ public interface Visitor<R> {
     R visit(IntegerExpression e);
     R visit(FloatExpression e);
     R visit(BooleanExpression e);
+    R visit(CharExpression e);
     R visit(Variable e);
     R visit(AdditionExpression e);
     R visit(EqualityExpression e);

src/test/java/CharTest.java

@@ -0,0 +1,164 @@
+import de.hsrm.compiler.Klang.ContextAnalysis;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class CharTest {
+
+    @Test
+    void shouldNotThrowIfComparingCharsEquality() {
+        // given
+        var tree = Helper.prepareParser("""
+                function bar(): int {
+                    let b: char = 'b';
+                    if ('a' == b) {
+                      return 1;
+                    }
+                    return -1;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfComparingCharsInequality() {
+        // given
+        var tree = Helper.prepareParser("""
+                function bar(): int {
+                    let b: char = 'b';
+                    if ('a' > b) {
+                      return 1;
+                    }
+                    return -1;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfCharLiteralIsAssignedToCharVariable() {
+        // given
+        var tree = Helper.prepareParser("""
+                function bar(): int {
+                    let c: char = 'c';
+                    return 1;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfCharLiteralIsReturnedFromFunction() {
+        // given
+        var tree = Helper.prepareParser("""
+                function bar(): char {
+                    return 'c';
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldNotThrowIfCharIsUsedInStruct() {
+        // given
+        var tree = Helper.prepareParser("""
+                struct myChar { c: char; }
+                function bar(): myChar {
+                    let x: myChar = create myChar('c');
+                    return x;
+                }
+                bar();
+                """);
+        var ctxAnal = new ContextAnalysis(Helper.getFuncs(tree), Helper.getStructs(tree), Helper.getEnums(tree));
+
+        // when / then
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldThrowIfCharIsAssignedToOtherTypedVariable() {
+        // given
+        var tree = Helper.prepareParser("""
+                struct foo { f: float; }
+                function bar(): int {
+                    let c: foo = 'c';
+                    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 3:4 Type mismatch: cannot combine foo and char", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowWhenReturningCharFromOtherTypedFunction() {
+        // given
+        var tree = Helper.prepareParser("""
+                function bar(): float {
+                    return 'c';
+                }
+                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 2:4 Type mismatch: cannot combine float and char", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowPassingCharToOtherTypedFunctionParameter() {
+        // given
+        var tree = Helper.prepareParser("""
+                function foo(a: float): void {
+                    let x: bool = false;
+                }
+                function bar(): void {
+                    foo('c');
+                }
+                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 argument 0 Expected float but got: char", e.getMessage());
+    }
+
+    @Test
+    void shouldThrowWhenAssigningCharToOtherTypedStructField() {
+        // given
+        var tree = Helper.prepareParser("""
+                struct foo { a: bool; }
+                function bar(): void {
+                    let x: foo = create foo(false);
+                    x.a = 'c';
+                }
+                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 4:4 Type mismatch: cannot combine bool and char", e.getMessage());
+    }
+}

src/test/java/ConstructorCallTest.java

@@ -21,7 +21,7 @@ public class ConstructorCallTest {
     }
 
     @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);
@@ -41,6 +41,6 @@ public class ConstructorCallTest {
         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

@@ -17,6 +17,6 @@ public class DestroyStatementTest {
         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

@@ -17,7 +17,7 @@ public class FieldAssignmentTest {
         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
@@ -29,6 +29,6 @@ public class FieldAssignmentTest {
         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

@@ -33,7 +33,7 @@ public class FunctionCallTest {
     }
 
     @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);

src/test/java/FunctionDefinitionTest.java

@@ -92,4 +92,28 @@ public class FunctionDefinitionTest {
         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/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/StructFieldAccessTest.java

@@ -16,7 +16,7 @@ public class StructFieldAccessTest {
         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
@@ -28,6 +28,6 @@ public class StructFieldAccessTest {
         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

@@ -17,6 +17,6 @@ public class VariableAssignmentTest {
         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

@@ -89,7 +89,7 @@ public class VariableDeclarationTest {
 
         // when / then
         var e = assertThrows(RuntimeException.class, () -> ctxAnal.visit(tree));
-        assertEquals("Error in line 1:34 Redeclaration of variable with name \"x\".", e.getMessage());
+        assertEquals("Error in line 1:34 Redeclaration of variable or parameter with name \"x\".", e.getMessage());
     }
 
     @Test

src/test/java/VariableTest.java

@@ -17,7 +17,7 @@ public class VariableTest {
         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

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);
 }

src/test/struct/struct.h

@@ -28,4 +28,6 @@ long getStructFieldRecA(struct testStructRec *t);
 struct testStructRec *getStructFieldRecB(struct testStructRec *t);
 
 struct testStructRec *setStructFieldRecA(struct testStructRec *t, long a);
-struct testStructRec *setStructFieldRecB(struct testStructRec *t, struct testStructRec *b);
+struct testStructRec *setStructFieldRecB(struct testStructRec *t, struct testStructRec *b);
+
+long isStackAlignedBeforeFunctionCall();

src/test/test.k

@@ -555,6 +555,72 @@ function getTestStructRec(a: int, b: testStructRec): testStructRec {
   return create testStructRec(a, b);
 }
 
+struct evenFieldsStruct {
+  a: int;
+  b: int;
+}
+
+struct oddFieldsStruct {
+  a: int;
+  b: int;
+  c: int;
+}
+
+function stackAlignmentTestInternal1(): oddFieldsStruct {
+  // an odd amount of constructor parameters could lead to an unaligned stack
+  // which results in a segmentation fault when calling malloc
+  return create oddFieldsStruct(1, 1, 1);
+}
+
+function stackAlignmentTestInternal2(): evenFieldsStruct {
+  // an odd amount of local variables could lead to an unaligned stack
+  // which results in a segmentation fault when calling malloc
+  let a: evenFieldsStruct = create evenFieldsStruct(1, 1);
+  return a;
+}
+
+function stackAlignmentTestInternal3(a: int): evenFieldsStruct {
+  // an odd amount of function parameters could lead to an unaligned stack
+  // which results in a segmentation fault when calling malloc
+  return create evenFieldsStruct(1, 1);
+}
+
+function stackAlignmentTestInternal4(a: int): evenFieldsStruct {
+  // if (function parameters + local variables + constructor parameters) is odd
+  // then this could lead to an unaligned stack
+  // which results in a segmentation faul when calling malloc
+  let b: int = 0;
+  let c: int = 0;
+  return create evenFieldsStruct(1, 1);
+}
+
+function stackAlignmentTestInternal5(a: int, b: int): evenFieldsStruct {
+  // if (function parameters + local variables + constructor parameters) is odd
+  // then this could lead to an unaligned stack
+  // which results in a segmentation faul when calling malloc
+  let c: int = 0;
+  return create evenFieldsStruct(1, 1);
+}
+
+function stackAlignmentTestInternal6(a: int, b: int): oddFieldsStruct {
+  // if (function parameters + local variables + constructor parameters) is odd
+  // then this could lead to an unaligned stack
+  // which results in a segmentation faul when calling malloc
+  let c: int = 0;
+  let d: int = 0;
+  return create oddFieldsStruct(1, 1, 1);
+}
+
+function isStackAlignedBeforeFunctionCall(): int {
+  let a: oddFieldsStruct = stackAlignmentTestInternal1();
+  let b: evenFieldsStruct = stackAlignmentTestInternal2();
+  let c: evenFieldsStruct = stackAlignmentTestInternal3(1);
+  let d: evenFieldsStruct = stackAlignmentTestInternal4(1);
+  let e: evenFieldsStruct = stackAlignmentTestInternal5(1, 1);
+  let f: oddFieldsStruct = stackAlignmentTestInternal6(1, 1);
+  return 1;
+}
+
 function getStructFieldA(t: testStruct): int {
   return t.a;
 }