From cb4ab121283e690506aa6bf17abb6fd5b8142107 Mon Sep 17 00:00:00 2001
From: Jordan Eldredge <jordan@jordaneldredge.com>
Date: Wed, 11 Sep 2019 20:36:46 -0700
Subject: [PATCH] Improve error message for missing opcode

---
 modern/src/maki-interpreter/parser.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/modern/src/maki-interpreter/parser.js b/modern/src/maki-interpreter/parser.js
index d5c1abc5..669bbf91 100644
--- a/modern/src/maki-interpreter/parser.js
+++ b/modern/src/maki-interpreter/parser.js
@@ -12,8 +12,12 @@ const PRIMITIVE_TYPES = {
 
 // TODO: Don't depend upon COMMANDS
 function opcodeToArgType(opcode) {
-  const argType = COMMANDS[opcode].arg;
-  switch (argType) {
+  const command = COMMANDS[opcode];
+  if (command == null) {
+    throw new Error(`Unknown opcode ${opcode}`);
+  }
+
+  switch (command.arg) {
     case "func":
     case "line":
       return "COMMAND_OFFSET";