Hal Daume III <hdaume@ISI.EDU> writes:

Hi all,

I don't think I can do this, but I figured I'd ask anyway. Suppose I have:

...

data X = X | Y | Z

and I want to match against a list of Xs. But all I want is to ensure that there's a Y followed by a Z, but I don't care if there's anything else (or lots of other stuff) in between. Namely, I want to match:

.*Y.*Z.*

I think that http://www.dcs.gla.ac.uk/~meurig/regexp has some stuff for you

Now, I can match YZ.* easily with:

...

foo (X:Y:_) = ...

furthermore, my matches never require any backtracking, so you won't see something like ".*X.*Y.*X.*Z" which could possibly make you backtrack (so, there are no duplicates in what I'm matching against).

Anway, the current way I do this is by having a function:

...

match [] _ = True match (m:ms) (x:xs) | m == x = match ms xs | otherwise = match (m:ms) xs

(Actually, I do a bit more -- I return Maybe [Int] where Nothing signifies that the match failed and Just intList specifies the indices of the matched elements, but this is superfluous).

so this requires me to write things like:

...

foo l | Just indices <- [X,Y] `match` l = let [x,y] = map (l!!) indices in ...

instead of the nice haskellesque syntax:

...

foo [..,x@X,..,y@Y,..] = ...

anyway, I'm curious if anyone else has pounded against this wall at all and if there's any tool (drift, or something perhaps) that would allow me to write more succinct versions?

Thanks!

- Hal

-- Hal Daume III

"Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

_______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell

-- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**