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

[Marco Antoniotti]

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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