Fix type error due to mutating ast element

Author: Steffen Märcker

prism/src/parser/ast/Expression.java

@@ -75,15 +75,21 @@ public String getResultName()
 	 * when evaluated during model checking?
 	 */
 	public abstract boolean returnsSingleValue();
-	
-	// Override version of deepCopy() from superclass ASTElement (to reduce casting).
 
+	// Override version of deepCopy() from superclass (to reduce casting).
 	@Override
 	public Expression deepCopy()
 	{
 		return (Expression) super.deepCopy();
 	}
 
+	// Override version of clone() from superclass (to reduce casting).
+	@Override
+	public Expression clone()
+	{
+		return (Expression) super.clone();
+	}
+
 	// Utility methods:
 
 	/**

prism/src/parser/visitor/Simplify.java

@@ -93,13 +93,15 @@ public Object visitNow(ExpressionBinaryOp e) throws PrismLangException
 				return e.getOperand2();
 			if (Expression.isDouble(e.getOperand2()) && e.getOperand2().evaluateDouble() == 0.0) {
 				// Need to be careful that type is preserved
-				e.getOperand1().setType(e.getType());
-				return e.getOperand1();
+				Expression op = e.getOperand1().clone();
+				op.setType(e.getType());
+				return op;
 			}
 			if (Expression.isDouble(e.getOperand1()) && e.getOperand1().evaluateDouble() == 0.0) {
 				// Need to be careful that type is preserved
-				e.getOperand2().setType(e.getType());
-				return e.getOperand2();
+				Expression op = e.getOperand2().clone();
+				op.setType(e.getType());
+				return op;
 			}
 			break;
 		case ExpressionBinaryOp.MINUS:
@@ -113,8 +115,9 @@ public Object visitNow(ExpressionBinaryOp e) throws PrismLangException
 			}
 			if (Expression.isDouble(e.getOperand2()) && e.getOperand2().evaluateDouble() == 0.0) {
 				// Need to be careful that type is preserved
-				e.getOperand1().setType(e.getType());
-				return e.getOperand1();
+				Expression op = e.getOperand1().clone();
+				op.setType(e.getType());
+				return op;
 			}
 			if (Expression.isDouble(e.getOperand1()) && e.getOperand1().evaluateDouble() == 0.0) {
 				ExpressionUnaryOp simplified = new ExpressionUnaryOp(ExpressionUnaryOp.MINUS, e.getOperand2());
@@ -130,13 +133,15 @@ public Object visitNow(ExpressionBinaryOp e) throws PrismLangException
 				return e.getOperand2();
 			if (Expression.isDouble(e.getOperand2()) && e.getOperand2().evaluateDouble() == 1.0) {
 				// Need to be careful that type is preserved
-				e.getOperand1().setType(e.getType());
-				return e.getOperand1();
+				Expression op = e.getOperand1().clone();
+				op.setType(e.getType());
+				return op;
 			}
 			if (Expression.isDouble(e.getOperand1()) && e.getOperand1().evaluateDouble() == 1.0) {
 				// Need to be careful that type is preserved
-				e.getOperand2().setType(e.getType());
-				return e.getOperand2();
+				Expression op = e.getOperand2().clone();
+				op.setType(e.getType());
+				return op;
 			}
 			if (Expression.isInt(e.getOperand2()) && e.getOperand2().evaluateInt() == 0) {
 				// Need to be careful that type is preserved