4 ms·

You want pure I/O in an untyped language. DCGs are the easiest way to have that (although they also have their limits).

by rscho 4y ago

nerdponx 4y ago
What do you mean by "pure I/O" in this case? And how does logic programming help with that? I've seen things like this in the context of "algebraic effects", where instead of performing I/O (and instead of using monadic I/O) you build up what amounts to an execution graph of effectful operations, which is then "interpreted" at runtime. Is that what you're describing?
- rscho 4y ago
  No, what I'm describing is the "monadic" behaviour of `phrase_from_file/2` and similar predicates. In conjunction with definite clause grammars, this means that your I/O operations either conform to the provided spec or fail. This is a "hot topic" (if LP topics can really still be "hot") and sees active development in new prolog systems. Check this out for prolog: https://youtu.be/Dqpxy4W7fAo https://youtu.be/Dqpxy4W7fAo https://www.swi-prolog.org/pldoc/man?section=pio https://www.swi-prolog.org/pldoc/man?section=pio https://github.com/mthom/scryer-prolog/blob/084fc845902f7b435b0e5e44aaeba023bc28958f/src/lib/pio.pl https://github.com/mthom/scryer-prolog/blob/084fc845902f7b43... "New" stuff in the MiniKanren world: https://staff.fnwi.uva.nl/c.u.grelck/nl-fp-talks/kourzanov.pdf https://staff.fnwi.uva.nl/c.u.grelck/nl-fp-talks/kourzanov.p... https://ifl2014.github.io/submissions/ifl2014_submission_18.pdf https://ifl2014.github.io/submissions/ifl2014_submission_18....
  - YeGoblynQueenne 4y ago
    (Not the OP) Thanks for the links, because 14 years after I first started coding in Prolog I'm still not sure what Pure I/O is or why it is. I mean, my intuition is that a file is a stream of bytes and wading through that stream is not going to be "pure" no matter what, just because a byte is not a concept in First Order Logic. But, OK, "pure" Prolog is not the same as FOL anyway, and so I may be convinced otherwise when I have the chance to peruse your links. So thanks again and sorry for any negative vibes emanating from my comment.
    - rscho 4y ago
      "pure" prolog I/O is every bit as pure as Haskell pure I/O, which is ... not very much and in a hand-wavy sort of way. My understanding is that it basically means "either it corresponds to the spec, or it fails". At first, it seems trivial and a strange point of pride to have. Until you realize that most languages actually don't have anything built-in to do that, and must resort to some sort of parser. At which point, the data is already past your I/O gateway and may lead to unpredictable effects in your program. This is not an academic opinion, just my 2c.
      - YeGoblynQueenne 4y ago
        Thanks for taking the time to reply! I appreciate your 2c. I guess my confusion about pure I/O stems from the documentation of phrase_from_file/2 in SWI-Prolog. The documentation says the predicate is for pure I/O and how it was implemented, and by whom, but it doesn't say what pure I/O is, and why it is needed. I guess the information is somewhere in one (or more) of the canonical Prolog textbooks, which I've only read several years ago (though multiple times over, each). I have to confess also I'm not much of a purist. My Prolog code looks like bog standard imperative code where I feel it doesn't really matter (e.g. I don't have any prejudice about setof/3 or maplist/2 over findall/3), and I guess file I/O is one of those cases. Anyway, thanks again, for your links and explanation. I owe you a quantum of knowledge :)

You want pure I/O in an untyped language. DCGs are the easiest way to have that (although they also have their limits).

by rscho 4y ago

You want pure I/O in an untyped language. DCGs are the easiest way to have that (although they also have their limits).

What do you mean by "pure I/O" in this case? And how does logic programming help with that? I've seen things like this in the context of "algebraic effects", where instead of performing I/O (and instead of using monadic I/O) you build up what amounts to an execution graph of effectful operations, which is then "interpreted" at runtime. Is that what you're describing?

rscho 4y ago
No, what I'm describing is the "monadic" behaviour of `phrase_from_file/2` and similar predicates. In conjunction with definite clause grammars, this means that your I/O operations either conform to the provided spec or fail. This is a "hot topic" (if LP topics can really still be "hot") and sees active development in new prolog systems. Check this out for prolog: https://youtu.be/Dqpxy4W7fAo https://youtu.be/Dqpxy4W7fAo https://www.swi-prolog.org/pldoc/man?section=pio https://www.swi-prolog.org/pldoc/man?section=pio https://github.com/mthom/scryer-prolog/blob/084fc845902f7b435b0e5e44aaeba023bc28958f/src/lib/pio.pl https://github.com/mthom/scryer-prolog/blob/084fc845902f7b43... "New" stuff in the MiniKanren world: https://staff.fnwi.uva.nl/c.u.grelck/nl-fp-talks/kourzanov.pdf https://staff.fnwi.uva.nl/c.u.grelck/nl-fp-talks/kourzanov.p... https://ifl2014.github.io/submissions/ifl2014_submission_18.pdf https://ifl2014.github.io/submissions/ifl2014_submission_18....
- YeGoblynQueenne 4y ago
  (Not the OP) Thanks for the links, because 14 years after I first started coding in Prolog I'm still not sure what Pure I/O is or why it is. I mean, my intuition is that a file is a stream of bytes and wading through that stream is not going to be "pure" no matter what, just because a byte is not a concept in First Order Logic. But, OK, "pure" Prolog is not the same as FOL anyway, and so I may be convinced otherwise when I have the chance to peruse your links. So thanks again and sorry for any negative vibes emanating from my comment.
  - rscho 4y ago
    "pure" prolog I/O is every bit as pure as Haskell pure I/O, which is ... not very much and in a hand-wavy sort of way. My understanding is that it basically means "either it corresponds to the spec, or it fails". At first, it seems trivial and a strange point of pride to have. Until you realize that most languages actually don't have anything built-in to do that, and must resort to some sort of parser. At which point, the data is already past your I/O gateway and may lead to unpredictable effects in your program. This is not an academic opinion, just my 2c.
    - YeGoblynQueenne 4y ago
      Thanks for taking the time to reply! I appreciate your 2c. I guess my confusion about pure I/O stems from the documentation of phrase_from_file/2 in SWI-Prolog. The documentation says the predicate is for pure I/O and how it was implemented, and by whom, but it doesn't say what pure I/O is, and why it is needed. I guess the information is somewhere in one (or more) of the canonical Prolog textbooks, which I've only read several years ago (though multiple times over, each). I have to confess also I'm not much of a purist. My Prolog code looks like bog standard imperative code where I feel it doesn't really matter (e.g. I don't have any prejudice about setof/3 or maplist/2 over findall/3), and I guess file I/O is one of those cases. Anyway, thanks again, for your links and explanation. I owe you a quantum of knowledge :)