[Haskell-cafe] Re: Subsequence near solved hopefully

[Remi Turk]

On Sun, Oct 17, 2004 at 10:53:37PM +0100, Sam Mason wrote:
> Peter Simons wrote:
> >This version should do it:
> >
> >isSubSeq :: (Eq a) => [a] -> [a] -> Bool
> >isSubSeq   []     _    = True
> >isSubSeq   _     []    = False
> >isSubSeq (x:xs) (y:ys)
> >  | x == y    = isSubSeq xs ys
>                  ^^^^^^^^
> 
> I think you want to refer to List.isPrefixOf here - your version is a
> sort of "ordered subset" test.  I.e. I get:
> 
>    "abc"  `isSubSeq`  ".a.b.c."   ===>   True

as Ketil pointed out, this "subsequence" test may be exactly what
the OP meant.

> My version would've been:
> 
>   isSubSeq x = any (isPrefixOf x) . tails
> 
> But Remi beat me to it (and for that I'll never forgive him! :-).
> 
>   Sam

But I only gave the point-free and the point-wise version: You
did the half-of-a-point version ;) (which I would actually have
used myself too) *ducks and runs*[1]

Groetjes,
Remi


[1] and falls asleep


-- 
Nobody can be exactly like me. Even I have trouble doing it.