Re: [Haskell-cafe] Suspected stupid Haskell Question

I wrote:

When you can assume Ord, the standard solution is, as you suggest, something like...

Oops, sorry, doesn't typecheck. Here it is corrected:

import qualified Data.Map as M import Data.List

histogram = M.toList . foldl' (\m x -> M.insertWith' (+) x 1 m) M.empty

This should work efficiently, with the right amount of laziness, even for very large lists.

Stuart's Arrows thing is much nicer when your list is small enough to be held in memory all at once. -Yitz