Re: [Haskell-beginners] lifting to applicative: recomputing an argument each time it is used?

On Sat, Sep 8, 2012 at 4:49 PM, Iain Nicol wrote:

Hi,

I think I'm trying to lift 'Data.List.intersperse' (to applicative or a monad) in such a way that its (first) argument is recomputed each time it is used. I'm hoping that there's a reusable, elegant or abstract, approach for this that I'm unaware of.

Instead of using intersperse, just generate two list and interlace them (interlace is easy to write, though not in Data.List :

interlace (x:xs) (y:ys) = x : y : interlace xs ys interlace xs [] = xs interlace [] ys = ys

listOfN n g = replicateM n g

mixIntersperse genSep genWord = do n <- arbitrary ws <- listOfN n genWord ss <- listOfN (n-1) genSep return $ interlace ws ss

That seems more elegant to me but you'll judge :) -- Jedaï