feat: add error message for variable redefenition attempt

exl/00_variables.fzs

@@ -16,7 +16,7 @@ printline(c);
 // Also, there is many different types to help your program
 //  work with many things:
 int signedInteger;
-uint unsignedInteger
+uint unsignedInteger;
 str string;
 bool boolean;
 

src/compiler/fzl_walker.c

@@ -1056,9 +1056,19 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
         if (res != FZL_SYMTABLE_RESULT_OK)
         {
           fzl_token_t *tok = node->var.identifier->token;
+          if (res == FZL_SYMTABLE_RESULT_EXISTS)
+          {
+            snprintf(wlast_err, sizeof(wlast_err),
+                     "'%s': cannot redefine '%s' at %ld:%ld", tok->filename,
+                     (char *)tok->value, tok->ln, tok->cn);
+          }
+          else
+          {
             snprintf(wlast_err, sizeof(wlast_err),
                      "'%s': cannot store '%s' at %ld:%ld", tok->filename,
                      (char *)tok->value, tok->ln, tok->cn);
+          }
+
           return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
         }
 
@@ -1225,6 +1235,11 @@ int fzl_walk(fzl_walker_t *walker)
   push_op(walker, FZL_OPCODE_RM_ENVTABLE);
 
   fin_ctx(walker);
+  if (walker->ctx)
+  {
+    while (walker->ctx)
+      fin_ctx(walker);
+  }
 
   if (result.error && !wlast_err[0])
     snprintf(wlast_err, sizeof(wlast_err), "%s", result.error_msg);