Proposal: Make Data.Map.insertWith' and friends consistently force the value inserted

[Felipe Lessa]

On Sun, May 30, 2010 at 11:34:47PM +0100, Ian Lynagh wrote:
> Hi all,
>
> Currently, Data.Map.insertWith' (and friends) only force the value
> inserted when the combining function creates it:
>
>     Prelude Data.Map> insertWith' (+) "foo" undefined empty `seq` ()
>     ()
>     Prelude Data.Map> insertWith' (+) "foo" undefined (singleton "foo" 1) `seq` ()
>     *** Exception: Prelude.undefined
>
> I think it would be more consistent for it to always force it:
>
>     Prelude Data.Map> insertWith' (+) "foo" undefined empty `seq` ()
>     *** Exception: Prelude.undefined
>     Prelude Data.Map> insertWith' (+) "foo" undefined (singleton "foo" 1) `seq` ()
>     *** Exception: Prelude.undefined

The current behaviour is unexpected.

+1 for the patch.

--
Felipe.