Re: [Caml-list] Pattern matching and strings

[Luc Maranget <luc.maranget@inria.fr>]

> I have to do a little bit of pattern matching on strings. My
 > first instict was to write something like the following.
 >
 > let foo x = ...
 > let bar x = ...
 > ... = function
 > | "foo" ^ rest -> foo rest
 > | "bar" ^ rest -> bar rest
 > | _ -> raise Unrecognized


I have thought about that a little.

My first guess is that such matching should be distinct from
ordinary PM, mixing the two would be an implementor nightmare.

My second guess is that what you want is regexp matching + a construct
for binding subparts of the matched string (maybe I am wrong here).

Using ocamllex syntax for patterns (+ as) your exemple could be written

regexpmatch s with
| "foo" (_* as x)  -> foo x
| "bar" (_* as x)  -> bar x
| _*               -> raise Unrecognized


This would be much nicer than using various regexp packages API, the
real add-on being the variables in place of \1, \2 etc.

Of course this would work only in the case where all patterns are known
statically and implementation is not 100% trivial, if you want some
warnings and compile-time production of matching automata.
(ie if you do not rely on regexp package).

In fact such, an extension is probably feasible using camlp4 and this
would probably be the best solution, to avoid extra-complexity in the
compiler itself.


In the end, do not hold your breath. I won't probably do that.
But it can be a interesting project for a compiler course...

--Luc



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