message: error: TS2339 [ERROR]: Property 'pos' does not exist on type 'never'.
diff: @@ -319,7 +319,7 @@ function checkOp(env: Env, instr: bril.Operation) {
  function checkConst(instr: bril.Constant) {
  if (!('type' in instr)) {
  - err(`const missing type`, instr!.pos);
  + err(`const missing type`, instr.pos);
  return;
  }
  if (typeof instr.type !== 'string') {
  