> 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.
Speaking of the laziness constraint, the simplest solution to the
strictness of dwBackwards (solution 1) would be to use irrefutable
pattern matching in the combine function:
dwBackwards predicate = fst . foldr combine ([],[]) where
-- Note the tilde in the next line...
combine x ~(ys,xs)
| predicate x = (ys, x:xs)
| otherwise = (x:xs, x:xs)
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