Scryer Prolog totally clueless how DCGs work

From	Mild Shock <janburse@fastmail.fm>
Newsgroups	comp.lang.prolog
Subject	Scryer Prolog totally clueless how DCGs work
Date	2025-07-09 11:33 +0200
Message-ID	<104ld1i$1vsct$1@solani.org> (permalink)

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Woa! This nonsense really made my day:

https://github.com/mthom/scryer-prolog/discussions/3004

It starts with, where somebody "tried" a declarative DCG
using constraint logic programming:

number_tail(0, 0) --> [].
number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit),
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.

He then noticed that its not deterministic. And since
it is not deterministic, clause ordering changes the
result when onced via once/1.

LoL

If DCGs had a cut, one would any way do:

number_tail(Number, DigitsCount) -->
   ("," | ""),
   digit(Digit), !,
   number_tail(Digits, RestDigitsCount),
   {
     DigitsCount #= RestDigitsCount + 1,
     Number #= Digit * 10 ^ RestDigitsCount + Digits
   }.
number_tail(0, 0) --> [].

Push the determinancy into the DCG. Otherwise you have
an explosion of choice points, and a lot of things go
totally wrong.

But the new DCG standard has no cut (!)/2.

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Scryer Prolog totally clueless how DCGs work Mild Shock <janburse@fastmail.fm> - 2025-07-09 11:33 +0200
  Lets see what the "experts" say (Was: Scryer Prolog totally clueless how DCGs work) Mild Shock <janburse@fastmail.fm> - 2025-07-09 11:36 +0200
    Payed Ass-Lickers all around (Was: Lets see what the "experts" say) Mild Shock <janburse@fastmail.fm> - 2025-07-09 11:38 +0200
      Its all about the money, not about quality (Was: Payed Ass-Lickers all around) Mild Shock <janburse@fastmail.fm> - 2025-07-09 11:42 +0200
        A case of dumbification by committee membership? (Was: Its all about the money, not about quality) Mild Shock <janburse@fastmail.fm> - 2025-07-09 20:01 +0200
    The stack overflow user by the name false (Was: Lets see what the "experts" say) Mild Shock <janburse@fastmail.fm> - 2025-07-15 11:50 +0200
      The choice is a little arbitrary from one angle (Re: The stack overflow user by the name false) Mild Shock <janburse@fastmail.fm> - 2025-07-15 11:59 +0200
  Does Scryer Prolog have all tricks up its sleeves? [Occurs Check] (Was: Scryer Prolog totally clueless how DCGs work) Mild Shock <janburse@fastmail.fm> - 2025-08-04 19:47 +0200

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