How do you catch the lisp programmer's error:

"I typed let, but I really meant let* and wasted five to ten seconds for the nth time today!"

I make this mistake all the time. Usually in a hurry or not anticipating the dependence of symbols I'm declaring I'll write:

(let ((foo-bar 42)
      (baz-bat (* foo-bar 2))
  (message "I bet you forgot something!"))

Resulting in the irritation in realizing that I miskeyed let* yet again.

Lisp error: (void-variable foo-bar)
  • 1
    – wasamasa
    Dec 14, 2016 at 8:12
  • 1
    That "irritating error" is exactly what helps you understand your mistake, no? Just what is your question? Is it how to prevent your making such a mistake?
    – Drew
    Dec 14, 2016 at 15:12
  • @Drew I was imprecise. My point is not a complaint of the error; the error itself is accurate and perfectly fine. The irritation is my frequent and fundamentally basic user error of misusing let in this particular fashion. I am interested in anything that serves to alert me to the fact or correct the issue before I eval-defun / test the code. Whether the solution is flycheck-style warnings, an autocorrect behavior, a personal policy of exclusively using let*, or something else-- I'm open to input. @wasamasa hit the nail on the head.
    – ebpa
    Dec 14, 2016 at 15:59

1 Answer 1


I'm aware of letcheck for this, but would prefer to have that kind of linting integrated into one of the tools Flycheck is using, ideally the byte-compiler itself. While one may argue that an unbound variable in a let that suspiciously looks like one of the previous bindings could still be resolved from outer scope, I severely doubt this will ever practically matter. Have you considered handing in a bug for this?

Personally, I just have it ingrained to return to the head of the let expression if I reuse a previous binding and correct it to let*.

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