Interesting idea. What would you expect to happen here? f x xs = let g y = x+y in map !! g xs Here I'm evaluating the function g hyperstrictly before the call to map. Does x, the free variable in g's function closure, get evaluated?
From an implementation point of view, you could imagine that hyperstrict evaluation would pull apart function closures, as well as data structures. But I'm not sure you could give that a sensible denotational semantics.
Simon
| -----Original Message-----
| From: haskell-prime-bounces@haskell.org
[mailto:haskell-prime-bounces@haskell.org] On Behalf Of
| Andy Gill
| Sent: 30 March 2006 23:12
| To: haskell-prime@haskell.org
| Cc: Laura McKinney
| Subject: deeqSeq proposal
|
| For the reasons talked about in previous posts, I'd like to propose a
| deepSeq
| for Haskell'.
|
| - It provides a mechanism to allow an effective, systematic
| tracking down of
| a class of space leaks.
| - It provides a mechanism to simply stomp on a class of space leaks.
| - It avoids the user having to explicitly declare instances for a
| homebrew deepSeq
| for every type in your program.
| - It has a declarative feel; this expression is hyper strict.
| - Is a specification of strictness.
| - It will open up various optimization opportunities, avoiding
| building thunks.
| (I dont talk about this more, but I'm happy to elaborate)
| - It can have an efficient implementation, or a simple (slow)
| implementation.
| (The fast implementation one can be used to stomp space leaks,
| the slow one can help find the same leaks.)
|
| What I would like to propose for Haskell' are four things:
|
| (Essential) Add a deepSeq function into Haskell'
|
| deepSeq :: a -> b -> b
|
| - Don't really care if its in a class or not; would prefer not
for
| the reasons John Hughes talked about.
| - This would deepSeq all its children for regular constructors.
| - deepSeq would not indirect into IO or MVar.
| - functions would be evaluated to (W?)HNF.
| - IO, ST are functions under the hood.
|
| (Easy) Add a $!! function, and a strict function
|
| f $!! a = a `deepSeq` f a
| strict a = a `deepSeq` a
|
| (Nice) Add a !! notation, where we have ! in datatypes.
|
| data StrictList a = Cons (!!a) (!!StrictList a) | Nil
|
| (Perhaps) Add a way of making *all* the fields strict/hyperstrict.
|
| data !!StrictList a = ..,
|
| We could also do this for !
|
| --------------
|
| Implementation:
|
| deepSeq (RAW_CONS