Fix refinement variable mapping: '_' and 'return' →

Author: RajShivu

liquidjava-verifier/src/main/java/liquidjava/rj_language/visitors/CreateASTVisitor.java

@@ -154,9 +154,25 @@ private Expression literalExpressionCreate(ParseTree rc) throws LJError {
             return new GroupExpression(create(((LitGroupContext) rc).literalExpression()));
         else if (rc instanceof LitContext)
             return create(((LitContext) rc).literal());
+
+        // else if (rc instanceof VarContext) {
+        // return new Var(((VarContext) rc).ID().getText());
+        // }
         else if (rc instanceof VarContext) {
-            return new Var(((VarContext) rc).ID().getText());
-        } else if (rc instanceof TargetInvocationContext) {
+            // Normalize return-value identifiers:
+            // - "return" (legacy syntax)
+            // - "_" (current shorthand)
+            // Both are mapped to "$result", the canonical return value identifier.
+            String name = ((VarContext) rc).ID().getText();
+            
+            if (name.equals("return") || name.equals("_")) {
+                name = "$result";
+            }
+
+            return new Var(name);
+        }
+
+        else if (rc instanceof TargetInvocationContext) {
             // TODO Finish Invocation with Target (a.len())
             return null;
         } else {