"result arity mismatch" when using a contract with or/c and values

[lojic]

I get the following error in the racket-mode REPL:

; result arity mismatch;
;  expected number of values not received
;   expected: 1
;   received: 2

When using a contract with or/c and values. Here is a small reproducible example:

#lang racket

(provide (contract-out
          [ foo
            (-> boolean? (or/c (values string? integer?)
                               (values #f #f))) ]))

(define (foo b)
  (if b
      (values "answer" 7)
      (values #f #f)))

An unsatisfactory workaround is to have values wrap the or/c instead of the or/c wrapping values, but that would allow, for example, (values string? #f) which is unacceptable.

The example compiles ok at the command line, but not in racket-mode.

Thanks!

Please copy all of the following lines and paste them into your bug report at https://github.com/greghendershott/racket-mode/issues/.

((alist-get 'racket-mode package-alist)
 #s(package-desc racket-mode
                 (20210727 1545)
                 "Racket editing, REPL, and more"
                 ((emacs
                   (25 1))
                  (faceup
                   (0 0 2))
                  (pos-tip
                   (20191127 1028)))
                 nil nil "/Users/badkins/.emacs.d/elpa/racket-mode-20210727.1545"
                 ((:url . "https://www.racket-mode.com/")
                  (:maintainer "Greg Hendershott")
                  (:authors
                   ("Greg Hendershott"))
                  (:commit . "ef9a3fed943495ec2b0c8258f8e00307d6434b17"))
                 nil))
((emacs-version "28.2")
 (system-type darwin)
 (x-gtk-use-system-tooltips UNDEFINED)
 (major-mode racket-repl-mode)
 (racket--el-source-dir "/Users/badkins/.emacs.d/elpa/racket-mode-20210727.1545/")
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 (racket-program "/Users/badkins/sync/github/racket/racket/bin/racket")
 (racket-command-timeout 10)
 (racket-path-from-emacs-to-racket-function identity)
 (racket-path-from-racket-to-emacs-function identity)
 (racket-browse-url-function racket-browse-url-using-temporary-file)
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 (racket-xp-after-change-refresh-delay 1)
 (racket-xp-mode-lighter
  (:eval
   (racket--xp-mode-lighter)))
 (racket-xp-highlight-unused-regexp "^[^_]")
 (racket-repl-buffer-name-function nil)
 (racket-submodules-to-run
  ((test)
   (main)))
 (racket-memory-limit 2048)
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  ((cm-accomplice . warning)
   (GC . info)
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   (racket/contract . error)
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   (* . fatal)))
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[lojic]

(sigh) it appears this is likely not a bug :( Although the example compiled ok, I received the same error at the command line that I did from racket-mode when I actually ran the app. I forgot that aspect of compiling in racket-mode vs. command line. I'll mark closed.

[greghendershott]

Although I might be misunderstanding, I think this is a run-time not compile-time error because or/c is a procedure, not syntax. And, at run-time, it's an error because a single procedure argument can't receive multiple values?

Having said all that if you gave me a pop-quiz I probably would have guessed wrongly that or/c is syntax not a procedure, and tried to write exactly what you reasonably wanted to write.

[lojic]

You are correct. I should've looked up or/c - I think I was just hoping the contract would magically work the way I wanted :) I think there is a way to get what I want with ->i, but in the end, I just went with the simpler (values (orc/c ...) (or/c ...)) as I have more pressing matters. Glad to know racket-mode is as solid as ever - I appreciate all you've done on it!