fix bug in repeated function calls

ast/eval.go

@@ -43,17 +43,16 @@ func (in *Token) Eval(funcs FuncTable, vars VarTable, cnvtUndefVars bool) *Token
 
     switch in.Tag {
     case BOOL, NUMBER, STRING:
-        res = in
+        res = in.Copy()
 
     case SYMBOL:
         res = GetVar(in.Value(), vars)
         if res == nil {
-            res = in
+            res = in.Copy()
 
             if GetFunction(in.Value(), funcs) == nil {
                 if cnvtUndefVars {
-                    in.Tag = STRING
-                    res = in
+                    res.Tag = STRING
                     break
                 }
 
@@ -63,19 +62,17 @@ func (in *Token) Eval(funcs FuncTable, vars VarTable, cnvtUndefVars bool) *Token
                 return nil
             }
         }
-        res.Next = in.Next
-
 
     case LIST:
         inner := in.Expand()
         if inner == nil {
-            res = in
+            res = in.Copy()
             break
         }
 
         if inner.Tag != SYMBOL {
             in.Direct(inner.Eval(funcs, vars, cnvtUndefVars))
-            res = in
+            res = in.Copy()
             break
         }
 

ast/token.go

@@ -48,6 +48,18 @@ func (t *Token) Append(arg *Token) {
     }
 }
 
+/* Shallow Copy
+ * in case of a LIST,
+ * inner will point to the same list.
+ */
+func (t *Token) Copy() *Token {
+    return &Token{
+        Tag: t.Tag,
+        inner: t.inner,
+        Next: t.Next,
+    }
+}
+
 /* Print function which is better suited for repl.
  * This one prints the SEXPRs as one would write them.
  * Does not evaluate tokens.