[Haskell-cafe] ANNOUNCE: The Monad.Reader - Issue 6

[David House]

On 31/01/07, Pixel <pixel at mandriva.com> wrote:
> i ended up with this one:
>
> dwBool predicate l = (foldr combine (\_ -> []) l) True
>     where
>       combine e fl beg = if beg && predicate e
>                          then fl True
>                          else e : fl False

Mine was:

dw :: (a -> Bool) -> [a] -> [a]
dw p = reverse . fst . foldl comb ([],False)
  where comb (xs,done) x | done      = (x:xs, True)
                         | p x       = (xs, False)
                         | otherwise = (x:xs, True)

Which is the simplest working algorithm I could come up with; sadly it
breaks the lazinesss constraint. It was a great article though, seeing
fix's definition in terms of foldr was one of those mind-bending
moments which makes learning Haskell what it is.

-- 
-David House, dmhouse at gmail.com