[Haskell-cafe] Suspected stupid Haskell Question

Yitzchak Gale gale at sefer.org
Wed Oct 17 07:38:42 EDT 2007

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.


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