From c3393ca2828b9f4eeef9f5b60ca6b45c1cd73c3e Mon Sep 17 00:00:00 2001
From: David Benn <dbenn@computer.org>
Date: Sun, 21 Jul 2024 20:29:59 +0930
Subject: [PATCH] #357: added a pop-with-error-message method to interpreter
 and used it in a refactoring of IS/BIND assignment cases

---
 .../tools/vstar/vela/VeLaInterpreter.java     | 34 +++++++++++--------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/src/org/aavso/tools/vstar/vela/VeLaInterpreter.java b/src/org/aavso/tools/vstar/vela/VeLaInterpreter.java
index 348b520b..06a2f11d 100644
--- a/src/org/aavso/tools/vstar/vela/VeLaInterpreter.java
+++ b/src/org/aavso/tools/vstar/vela/VeLaInterpreter.java
@@ -202,6 +202,21 @@ public Stack<Operand> getStack() {
         return stack;
     }
 
+    /**
+     * Pop and return an operand from the stack if not empty.
+     * 
+     * @param msgOnError The exception message to use if the stack is empty.
+     * @return The operand on top of the stack.
+     * @throws VeLaEvalError Thrown when the stack is empty.
+     */
+    public Operand pop(String msgOnError) throws VeLaEvalError {
+        if (!stack.isEmpty()) {
+            return stack.pop();
+        } else {
+            throw new VeLaEvalError(msgOnError);
+        }
+    }
+
     /**
      * VeLa program interpreter entry point.
      * 
@@ -580,23 +595,12 @@ private void specialForm(AST ast) {
             }
             break;
 
-        case BIND:
-            eval(ast.right());
-
-            String varName = ast.left().getToken();
-
-            if (!stack.isEmpty()) {
-                bind(varName, stack.pop(), false);
-            } else {
-                String msg = "No value to assign to \"" + varName + "\"";
-                throw new VeLaEvalError(msg);
-            }
-
-            break;
-
+        case BIND: 
         case IS:
             eval(ast.right());
-            bind(ast.left().getToken(), stack.pop(), true);
+            String varName = ast.left().getToken();
+            String msg = "No value to bind to \"" + varName + "\"";
+            bind(varName, pop(msg), ast.getOp() == Operation.IS);
             break;
 
         case FUNDEF: