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December 2012

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Re: [cl-unification-devel] MATCH and friends usage and changes
by Marco Antoniotti 04 Dec '12

04 Dec '12

On Dec 4, 2012, at 04:52 , Pixie <pix(a)kepibu.org> wrote: > On 2012.12.03 09:31, Marco Antoniotti wrote: >> Dear all (the few, the self-chosen :) lurking here) >> >> I have been fiddling about with a "pattern compiler" to be made part >> of a compiler-macro for MATCH-CASE. After reading a few things here >> and there, I came to the conclusion that for CL and CL-UNIFICATION >> there is no need for anything particularly sophisticated (things like >> "partial test/evaluation merging" and whatnot), but I also started to >> think that maybe it would be better to introduce new syntax. >> Something along the lines of >> >> (PAT (<object> &key …) <clauses>) >> >> Now. This may look simple, but suppose you wanted to do something >> like >> >> (let ((x 42)) (y 123)) (pat (x y) ((42 123) t) (_ 'not-matched))) >> >> Now, while in principle this is easy (you just have a "list" instead >> of an object as first element), things may become hairy very soon >> when you want to add keywords affecting the matching process (cfr the >> MATCH-CASE syntax >> >> match-case (<object> &key errorp default-substitution) <clauses> >> >> where grouping is used for the keyword variables errorp >> default-substitution). With this consideration in mind the above >> example would become >> >> (let ((x 42)) (y 123)) (pat ((x y)) ((42 123) t) (_ 'not-matched))) >> >> So the questions I have for you are two: (1) do you have any ideas >> about syntax, even at the cost of introducing some "spurious infix" >> bit? (2) the PAT above should be really be named MATCH-CASE, but >> that is already taken; for the sake of backward compatibility, do you >> think that PAT or CASE-MATCH or SELECT or whatever should be used for >> the new syntax? > > To be honest, I'm not sure I understand what problem you're trying to solve by adding this PAT thing. The extensibility of cl-unification via #t(...) is one of the things I love about it[1], and your PAT syntax doesn't appear to do much outside of lists--which, well, isn't that what the *F variants are for? Well, the PAT thingy is just a non-completely-backward-compatible version of MATCH-CASE. To tell the truth the problem is all there. Also, I have developed a form of Racket envy given their slew of match** forms. :) > Though if you're in the mood for cl-unification work, my cl-unification repo is still around[2], if you'd be interested in looking at and/or pulling patches from it. ;) Somewhere in the archives of this mailing list is a listing of what I changed and why. (Goodness, has it been several years already?!) Well, yes. In some ways this says that the library is pretty solid :) I believe I did incorporate at least some of your patches in the main trunk. I will have a look at your repo (and I should bite the bullet and just switch to git as main repository) and see what is still left out. > [1] Though I've mentioned in the pre-Quicklisp days it'd be nice to > have some named-readtable support. Any specifics? > [2] http://repo.kepibu.org/cl-unification/ -- It's a few patches behind > CVS at the moment, alas. Thanks. -- Marco Antoniotti

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[cl-unification-devel] MATCH and friends usage and changes
by Marco Antoniotti 03 Dec '12

03 Dec '12

Dear all (the few, the self-chosen :) lurking here) I have been fiddling about with a "pattern compiler" to be made part of a compiler-macro for MATCH-CASE. After reading a few things here and there, I came to the conclusion that for CL and CL-UNIFICATION there is no need for anything particularly sophisticated (things like "partial test/evaluation merging" and whatnot), but I also started to think that maybe it would be better to introduce new syntax. Something along the lines of (PAT (<object> &key …) <clauses>) Now. This may look simple, but suppose you wanted to do something like (let ((x 42)) (y 123)) (pat (x y) ((42 123) t) (_ 'not-matched))) Now, while in principle this is easy (you just have a "list" instead of an object as first element), things may become hairy very soon when you want to add keywords affecting the matching process (cfr the MATCH-CASE syntax match-case (<object> &key errorp default-substitution) <clauses> where grouping is used for the keyword variables errorp default-substitution). With this consideration in mind the above example would become (let ((x 42)) (y 123)) (pat ((x y)) ((42 123) t) (_ 'not-matched))) So the questions I have for you are two: (1) do you have any ideas about syntax, even at the cost of introducing some "spurious infix" bit? (2) the PAT above should be really be named MATCH-CASE, but that is already taken; for the sake of backward compatibility, do you think that PAT or CASE-MATCH or SELECT or whatever should be used for the new syntax? Cheers -- Marco Antoniotti

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