RFC: Should Data.IntMap.Strict be value-strict in the function arguments or the map itself
johan.tibell at gmail.com
Thu Oct 27 19:13:56 CEST 2011
On Thu, Oct 27, 2011 at 10:03 AM, Edward Z. Yang <ezyang at mit.edu> wrote:
> I'd like to remark that the situation with keys is not /quite/ comparable.
> Even if we don't need to look at the key for inserting into an empty map,
> it will get forced anyway because IntMaps are spine-strict (in particular,
> are strict in their keys.)
I'm not quite sure if I follow. Here's Data.IntMap.insert:
insert :: Key -> a -> IntMap a -> IntMap a
insert k x t = k `seq`
case t of
Bin p m l r
| nomatch k p m -> join k (Tip k x) p t
| zero k m -> Bin p m (insert k x l) r
| otherwise -> Bin p m l (insert k x r)
Tip ky _
| k==ky -> Tip k x
| otherwise -> join k (Tip k x) ky t
Nil -> Tip k x
Without the explicit `seq`
insert undefined 1 Nil
terminates but with the `seq` it's _|_.
Are you saying it will eventually get force if someone e.g. does a lookup
after the insert?
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