diff --git a/src/main/java/org/ntlab/rdlworkbench/ast/EnhancedForStatement.java b/src/main/java/org/ntlab/rdlworkbench/ast/EnhancedForStatement.java
index bad5636..9fe77ec 100644
--- a/src/main/java/org/ntlab/rdlworkbench/ast/EnhancedForStatement.java
+++ b/src/main/java/org/ntlab/rdlworkbench/ast/EnhancedForStatement.java
@@ -17,7 +17,7 @@
 
     @Override
     public String toString() {
-        String typeName = singleVariableDeclaration.getType().getImplementationTypeName();
+        String typeName = singleVariableDeclaration.getType().toString();
         return "for (" + typeName + " " + singleVariableDeclaration.getName() + " : " + expression + ") " + body;
     }
 }
diff --git a/src/main/java/org/ntlab/rdlworkbench/ast/InfixExpression.java b/src/main/java/org/ntlab/rdlworkbench/ast/InfixExpression.java
index b47f949..2a84e2d 100644
--- a/src/main/java/org/ntlab/rdlworkbench/ast/InfixExpression.java
+++ b/src/main/java/org/ntlab/rdlworkbench/ast/InfixExpression.java
@@ -1,19 +1,17 @@
 package org.ntlab.rdlworkbench.ast;
 
-import models.algebra.Symbol;
-
 /**
  * Represents an infix expression in AST (Abstract Syntax Tree)
  *
  * @author s-yamagiwa
  */
 public class InfixExpression extends Expression {
-	private Symbol operator;
+	private String operator;
 	
 	private Expression leftOperand;
 	private Expression rightOperand;
 	
-	public InfixExpression(Symbol operator, Expression leftOperand, Expression rightOperand) {
+	public InfixExpression(String operator, Expression leftOperand, Expression rightOperand) {
 		this.operator = operator;
 		this.leftOperand = leftOperand;
 		this.rightOperand = rightOperand;
@@ -24,11 +22,11 @@
 		return new InfixExpression(operator, leftOperand.replace(variable, expression), rightOperand.replace(variable, expression));
 	}
 	
-	public Symbol getOperator() {
+	public String getOperator() {
 		return this.operator;
 	}
 	
-	public void setOperator(Symbol operator) {
+	public void setOperator(String operator) {
 		this.operator = operator;
 	}
 	
@@ -50,6 +48,6 @@
 	
 	@Override
 	public String toString() {
-		return leftOperand.toString() + " " + operator.toString() + " " + rightOperand.toString();
+		return leftOperand.toString() + " " + operator + " " + rightOperand.toString();
 	}
 }
diff --git a/src/main/java/org/ntlab/rdlworkbench/ast/InterfaceDeclaration.java b/src/main/java/org/ntlab/rdlworkbench/ast/InterfaceDeclaration.java
index b2968e1..57e5188 100644
--- a/src/main/java/org/ntlab/rdlworkbench/ast/InterfaceDeclaration.java
+++ b/src/main/java/org/ntlab/rdlworkbench/ast/InterfaceDeclaration.java
@@ -49,7 +49,7 @@
             if (m.getReturnType() == null) {
                 signature += "void ";
             } else {
-                signature += m.getReturnType().getInterfaceTypeName() + " ";
+                signature += m.getReturnType().toString() + " ";
             }
             signature += m.getName() + "(";
             if (m.getParameters() != null) {