[HN Gopher] Continuations by example: Exceptions, time-traveling...
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Continuations by example: Exceptions, time-traveling search,
threads, and more
Author : alschwalm
Score : 111 points
Date : 2020-07-16 14:25 UTC (8 hours ago)
(HTM) web link (matt.might.net)
(TXT) w3m dump (matt.might.net)
| verytrivial wrote:
| I always start Matt Might articles thinking "Okay, THIS is the
| one I'm going to understand all the way to the very end without
| unlearning what I just read, else I die," and alas, I have again
| died.
| vincnetas wrote:
| Me to. Level failed, but then i found this cheat code from
| apache and at lest i now understand basics.
|
| http://commons.apache.org/sandbox/commons-javaflow/
| offbynull wrote:
| AFAIK Javaflow's been inactive for over a decade. Newer
| implementations for the same concept include
| https://github.com/offbynull/coroutines and
| https://github.com/vsilaev/tascalate-javaflow/.
|
| Full disclosure: I'm the one who built / owns the first
| project.
| joel_dice wrote:
| On the topic of inactive continuation implementations for
| Java: I implemented native support for both delimited
| (shift/reset) and non-delimited (call/cc) continuations in
| the Avian JVM. See https://github.com/ReadyTalk/avian/blob/
| master/test/extra/Co... for some mind-bending examples.
| dlo wrote:
| Love it. Lmk if you never need a hand. I was on the core
| analysis team at Fortify.
| sjtindell wrote:
| Thanks for sharing this background and cool project.
| azeirah wrote:
| 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.
| hencq wrote:
| 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...
| [deleted]
| [deleted]
| jolmg wrote:
| I think I've found a good use for continuations in a parser
| combinator library I'm writing, though I haven't gotten around to
| working on the corresponding feature yet.
|
| Has anyone used continuations in a serious/non-academic way?
| gus_massa wrote:
| I used to implement an equivalent of exit or return statement,
| like in this example. #lang racket ;
| implement sqrt in a very inefficient way (let/ec exit
| (for ([i 10]) (when (= (* i i) 49) (exit
| i))) "not found :(") ;==> 7
|
| There are more idiomatic and easy ways to write this, but when
| you have to many nested and not nested for's, sometimes it is
| useful to have a magical exit-everything-now.
| emmanueloga_ wrote:
| I was actually relieved when I found this article [1] which
| argues against call/cc as a core language feature. Alas, I think
| the argument does not dismiss _delimited continuations_, so now
| my burden has shifted from mastering call/cc to mastering
| shift/reset :-/ [2].
|
| 1: http://okmij.org/ftp/continuations/against-callcc.html
|
| 2: https://en.wikipedia.org/wiki/Delimited_continuation
| [deleted]
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