[Haskell-cafe] Efficient functional idiom for histogram

[Malcolm Wallace]

> In an imperative language like Python, I'd use a dictionary as an
> accumulator - something like
>
>    for el in input:
>        accums[i] = accums.get(i, 0) + 1

Haskell has efficient dictionary structures too, e.g. Data.Map

   List.foldl' (\m x-> Map.insertWith' (+) x 1 m) Map.empty

Regards,
     Malcolm