-1 for me too, for the reasons already discussed in the thread (i.e., because it makes it easy to accidentally ignore potentially important results). I think that gains in readability from this generalization are at best questionable.

-Iavor

On Tue, Jun 5, 2012 at 2:07 PM, Andres Löh <andres@well-typed.com> wrote:

> Btw. the mapM memory leak can be easily and accidentally resurrected by
> writing
>
> when_ b (mapM f xs)
>
> with
>
> f :: a -> m ()
> when_ :: Bool -> m a -> m ()

I don't understand the whole mapM analogy (yet). I don't need when_ to
get into trouble with using mapM. Also, whether a space leak with mapM
arises or not typically doesn't depend on whether you use its result
or not. It's the other way round: if you run mapM on a huge list but
aren't interested in the results, then you should use mapM_ instead.
So the problem here is accidentally producing a (large) result rather
than accidentally ignoring it.

Cheers,
Andres

--
Andres Löh, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

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