added boolean operators

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

@@ -0,0 +1,14 @@
+package de.hsrm.compiler.Klang.nodes.expressions;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class AndExpression extends BinaryExpression {
+    public AndExpression(Expression lhs, Expression rhs) {
+        super(lhs, rhs);
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}

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

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

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

@@ -0,0 +1,14 @@
+package de.hsrm.compiler.Klang.nodes.expressions;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class OrExpression extends BinaryExpression {
+    public OrExpression(Expression lhs, Expression rhs) {
+        super(lhs, rhs);
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+}