5 ms·

Reminds me of perl6. Why don't more languages support grammars like this? Fun example: https://github.com/perl6/perl6-examples/blob/master/categories/interpret

Reminds me of perl6. Why don't more languages support grammars like this? Fun example: https://github.com/perl6/perl6-examples/blob/master/categories/interpreters/lisp.pl#L34 https://github.com/perl6/perl6-examples/blob/master/categori...

throwaway7645 10y ago
Usually they do through a PEG library if you search for that. Lua has a nice one and Python a few ok ones. They aren't native to the language like Rebol and Perl6 though.
- wcummings 10y ago
  Yeah, I meant natively.
  - throwaway7645 10y ago
    Oh, yea. P6, Rebol, Red...any lisp with a little work.
    - draegtun 10y ago
      And Perl5. Here are two examples of grammar engines built out of perl regex... * Regexp::Grammars - https://metacpan.org/pod/Regexp::Grammars https://metacpan.org/pod/Regexp::Grammars * Parse::RecDescent - https://metacpan.org/pod/Parse::RecDescent https://metacpan.org/pod/Parse::RecDescent
      - throwaway7645 10y ago
        Yea, not native which is what the poster ended up meaning, but I hear that one you linked from Damian Conway is great.
        draegtun 10y ago
        No external library is used in these modules just Perl5 native regex engine. NB. I think thats also same for Parsec (built out of Haskell's parser combinators) BTW - Damian created both of them, Regexp::Grammars was his replacement for his Parse::RecDescent.
        throwaway7645 10y ago
        Interesting. I didn't know they had no dependencies. Is it still considered native though since you have to import another module? Rebol & Perl6 don't require that although I'm probably grasping at straws lol. Thanks for pointing out Damian replaced Parse::RecDescent with the other one as I was reading doc on it today at work.
        draegtun 10y ago
        You can write grammars in pure Perl5 regex but it can get a bit fugly :) Here's a (very) simple example I did in Perl5 - https://news.ycombinator.com/item?id=6895126 https://news.ycombinator.com/item?id=6895126 And here's a (nicer!) port to Rebol I also did - https://www.reddit.com/r/programming/comments/1smpa1/why_rebol_red_and_the_parse_dialect_are_cool/ce035cv/ https://www.reddit.com/r/programming/comments/1smpa1/why_reb...
        throwaway7645 10y ago
        Thank you!
draegtun 10y ago
Here's that fun example written in Rebol parse: digits: charset "1234567890" char: charset [#"a" - #"z" "+/-*"] ;; chars allowed in a symbol not-quot: complement charset {"} esc-string: [{\"} | not-quot] bool: ["#t" | "#f"] float: [opt "+-" any digits "." some digits] number: [opt "+-" some digits] symbol: [some char] quot: [#"'" [sexp | atom]] string: [{"} any esc-string {"}] statement: [sexp | atom | space | newline] sexp: ["(" any statement ")"] atom: [bool | float | number | quot | symbol | string] lisp-rule: [some statement] NB. I wrote this "off the cuff" so I don't expect it to be flawless! Also there are no capture rules provided in my example (unlike perl6 grammars which provides this automatically).
- yellowapple 10y ago
  It's worth noting that this grammar is a bit more restrictive than the Perl 6 equivalent. In particular, "\d" in Perl includes not only 0 through 9, but any Unicode character that's classified as a "digit". The Perl 6 grammar documentation features this in an example of using arbitrary methods in grammars: https://docs.perl6.org/language/grammars.html#Methods_in_Grammar https://docs.perl6.org/language/grammars.html#Methods_in_Gra...
  - draegtun 10y ago
    I think the Perl 6 example should really use [0-9] instead of \d because it's unlikely that unicode numerals are allowed (in the Common Lisp spec). Anyway neither example fully covers the Common Lisp spec for a number atom (for eg. scientific notation or rationals).
    - yellowapple 10y ago
      I don't think covering all of the Common Lisp spec is required to be Greenspun-compliant ;)
      - draegtun 10y ago
        In that case Rebol is already Greenspun-compliant ;-) (print (multiply (add 1 2) 3)) ... will print an answer of 9
heimp 10y ago
Rascal MPL is another one that comes to mind. http://www.rascal-mpl.org/ http://www.rascal-mpl.org/

throwaway7645 10y ago

Usually they do through a PEG library if you search for that. Lua has a nice one and Python a few ok ones. They aren't native to the language like Rebol and Perl6 though.

wcummings 10y ago
Yeah, I meant natively.
- throwaway7645 10y ago
  Oh, yea. P6, Rebol, Red...any lisp with a little work.
  - draegtun 10y ago
    And Perl5. Here are two examples of grammar engines built out of perl regex... * Regexp::Grammars - https://metacpan.org/pod/Regexp::Grammars https://metacpan.org/pod/Regexp::Grammars * Parse::RecDescent - https://metacpan.org/pod/Parse::RecDescent https://metacpan.org/pod/Parse::RecDescent
    - throwaway7645 10y ago
      Yea, not native which is what the poster ended up meaning, but I hear that one you linked from Damian Conway is great.
      - draegtun 10y ago
        No external library is used in these modules just Perl5 native regex engine. NB. I think thats also same for Parsec (built out of Haskell's parser combinators) BTW - Damian created both of them, Regexp::Grammars was his replacement for his Parse::RecDescent.
        throwaway7645 10y ago
        Interesting. I didn't know they had no dependencies. Is it still considered native though since you have to import another module? Rebol & Perl6 don't require that although I'm probably grasping at straws lol. Thanks for pointing out Damian replaced Parse::RecDescent with the other one as I was reading doc on it today at work.
        draegtun 10y ago
        You can write grammars in pure Perl5 regex but it can get a bit fugly :) Here's a (very) simple example I did in Perl5 - https://news.ycombinator.com/item?id=6895126 https://news.ycombinator.com/item?id=6895126 And here's a (nicer!) port to Rebol I also did - https://www.reddit.com/r/programming/comments/1smpa1/why_rebol_red_and_the_parse_dialect_are_cool/ce035cv/ https://www.reddit.com/r/programming/comments/1smpa1/why_reb...
        throwaway7645 10y ago
        Thank you!

draegtun 10y ago

Here's that fun example written in Rebol parse: digits: charset "1234567890" char: charset [#"a" - #"z" "+/-*"] ;; chars allowed in a symbol not-quot: complement charset {"} esc-string: [{\"} | not-quot] bool: ["#t" | "#f"] float: [opt "+-" any digits "." some digits] number: [opt "+-" some digits] symbol: [some char] quot: [#"'" [sexp | atom]] string: [{"} any esc-string {"}] statement: [sexp | atom | space | newline] sexp: ["(" any statement ")"] atom: [bool | float | number | quot | symbol | string] lisp-rule: [some statement] NB. I wrote this "off the cuff" so I don't expect it to be flawless! Also there are no capture rules provided in my example (unlike perl6 grammars which provides this automatically).

yellowapple 10y ago
It's worth noting that this grammar is a bit more restrictive than the Perl 6 equivalent. In particular, "\d" in Perl includes not only 0 through 9, but any Unicode character that's classified as a "digit". The Perl 6 grammar documentation features this in an example of using arbitrary methods in grammars: https://docs.perl6.org/language/grammars.html#Methods_in_Grammar https://docs.perl6.org/language/grammars.html#Methods_in_Gra...
- draegtun 10y ago
  I think the Perl 6 example should really use [0-9] instead of \d because it's unlikely that unicode numerals are allowed (in the Common Lisp spec). Anyway neither example fully covers the Common Lisp spec for a number atom (for eg. scientific notation or rationals).
  - yellowapple 10y ago
    I don't think covering all of the Common Lisp spec is required to be Greenspun-compliant ;)
    - draegtun 10y ago
      In that case Rebol is already Greenspun-compliant ;-) (print (multiply (add 1 2) 3)) ... will print an answer of 9

heimp 10y ago

Rascal MPL is another one that comes to mind. http://www.rascal-mpl.org/ http://www.rascal-mpl.org/