Continuations by example: Exceptions, time-traveling search, threads, and more

Re:Continuations by example: Exceptions, time-traveling sear... by azeirah on Thursday July 16, 2020 @05:24PM (#23863985)

I'm having an ADHD night and I had the same thought, except I haven't died yet. Felt like giving up three times already, but I did have a click moment after playing around with a scheme repl for a couple of minutes. I understand the first example of call/cc now!

  (display
    (call/cc (lambda (cc)
              (display "I got here.\n")
              (cc "This string was passed to the continuation.\n")
              (display "But not here.\n"))))

Edit: Tried playing around with mit-scheme, but it doesn't work with the ctrl-v'ing the examples. Chezscheme does work.

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Re:Continuations by example: Exceptions, time-traveling sear... by hencq on Thursday July 16, 2020 @06:13PM (#23864436)

It seems that MIT-Scheme needs the cc function to be a function of 1 argument (the return value for the continuation)[0]

Changing it to the following should work:

  (let ((start #f))
    (if (not start)
      (call/cc (lambda (cc)
                 (set! start cc))))
  
    (display "Going to invoke (start)\n")
    
    (start #f))

[0] https://www.gnu.org/software/mit-scheme/documentation/stable...

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Re:Continuations by example: Exceptions, time-traveling sear... by DonaldPShimoda on Thursday July 16, 2020 @07:50PM (#23865250)

For what it's worth, almost any time Matt writes about Scheme he's likely using Racket so it'd be worth trying that for his posts!

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