A related data type that I've made use of in the past is described here
https://www.fpcomplete.com/user/edwardk/snippets/once
This version has the benefit that it works with data that really does need
a deepSeq, but encapsulates it in such a way that subsequent deepSeq's do
no extra work.
-Edward
On Tue, Feb 10, 2015 at 3:46 AM, Edward Z. Yang
I propose the following (abstract) data type, functions, and instance be added to deepseq (naming amenable to bikeshedding):
newtype NF a = NF a -- abstract makeNF :: NFData a => a -> NF a getNF :: NF a -> a instance NFData (NF a) where rnf x = x `seq` ()
NF is an abstract data type representing data which has been evaluated to normal form; the guarantee specifically is, if NF is in whnf, then it is in nf. Crucially, when we have 'NF a', we ONLY need to seq it in order to assure that it is fully evaluated.
This guarantee is sufficient for a variety of cases where normal data is necessary, e.g. when transmitting data over Channels. For example, from the monad-par library 'put_' could be used in place of 'put' with this type signature.
put_ :: IVar (NF a) -> (NF a) -> Par ()
Cheers, Edward _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries