From haskell-cafe  Sat Nov 20 16:55:08 2004
From: Jorge Adriano Aires <jadrian () mat ! uc ! pt>
Date: Sat, 20 Nov 2004 16:55:08 +0000
To: haskell-cafe
Subject: Re: [Haskell-cafe] foldlWhile
Message-Id: <200411201655.08590.jadrian () mat ! uc ! pt>
X-MARC-Message: https://marc.info/?l=haskell-cafe&m=120491986638590

(opss just noticed I did a reply-to)

> > The following is closer to the original, but doesn't work when the whole
> > list is folded (i.e., p always satisfied):
> > foldlWhile f p a = head . dropWhile p . scanl f a
>
> Serge's version returns the last 'a' that satisfies 'p', while yours
Not really.

> returns the first 'a' that does not satisfy 'p'.  This should be an
> equivalent version:
Yeap, just like his, 

foldlWhile :: (a -> b -> a) -> (a -> Bool) -> a -> [b] -> a
foldlWhile    f                p              a    bs  =
<snip>
(_,     False) -> a
<snip>

It tests the accumulator with p, and returns it on "false".

J.A.