[cl-unification-devel] MATCH and friends usage and changes

[Pixie]

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?


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?!)


[1] Though I've mentioned in the pre-Quicklisp days it'd be nice to
     have some named-readtable support.
[2] http://repo.kepibu.org/cl-unification/ -- It's a few patches behind
     CVS at the moment, alas.