diff --git a/AlgebraicDataflowArchitectureModel/src/code/ast/PlainExpression.java b/AlgebraicDataflowArchitectureModel/src/code/ast/PlainExpression.java
index d00c3fa..2acdc57 100644
--- a/AlgebraicDataflowArchitectureModel/src/code/ast/PlainExpression.java
+++ b/AlgebraicDataflowArchitectureModel/src/code/ast/PlainExpression.java
@@ -10,6 +10,11 @@
 	public PlainExpression(String expression) {
 		this.expression = expression;
 	}
+
+	@Override
+	public Expression replace(Variable variable, Expression newExpression) {
+		return new PlainExpression(expression.replace(variable.toString(), newExpression.toString()));
+	}
 	
     @Override
     public String toString() {
diff --git a/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclaration.java b/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclaration.java
index b841603..58fad83 100644
--- a/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclaration.java
+++ b/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclaration.java
@@ -59,7 +59,7 @@
 
 	public String toString() {
 		String code = "";
-		code += variableName;
+		code += type.getInterfaceTypeName() + " " + variableName;
 		if (optionalInitializer != null) {
 			code += " = " + optionalInitializer;
 		}
diff --git a/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclarationStatement.java b/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclarationStatement.java
index a5f3c8a..9e8eb70 100644
--- a/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclarationStatement.java
+++ b/AlgebraicDataflowArchitectureModel/src/code/ast/VariableDeclarationStatement.java
@@ -67,7 +67,7 @@
         }
 
         if (this.type != null) {
-            sb.append(this.type.getImplementationTypeName()).append(" ");
+            sb.append(this.type.getInterfaceTypeName()).append(" ");
         }
 
         for (int i = 0; i < fragments.size(); i++) {