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.

+1 (Although a user can seq the value herself before calling insertWith'...) Regards, Bas P.S. I just noticed that Data.IntMap doesn't provide the strict insertWith' and insertWithKey' like Data.Map does. That seems to be a bit inconsistent. On Mon, May 31, 2010 at 12:34 AM, 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

Patch:

hunk ./Data/Map.hs 460  insertWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a  insertWithKey' f kx x t   = case t of -      Tip -> singleton kx x +      Tip -> singleton kx $! x       Bin sy ky y l r           -> case compare kx ky of                LT -> balance ky y (insertWithKey' f kx x l) r

Ticket: http://hackage.haskell.org/trac/ghc/ticket/4109

Suggested discussion deadline: 14 June 2010.

Thanks Ian

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