Re: Proposal: NF newtype

22 Apr 2015


      Only thing I can think of is adding a bunch of `deriving`s to NF. I can
picture people wanting to just plot an `NF` into the middle of their data
structures and still be able to `show` it for debugging. I'm guessing a
minimal list may be Show, Read, Eq, Ord, Typeable. Data and Generic seem
like an interesting case, since- on the one hand- it would be nice to have
the instances (especially the latter) for auto-deriving mechanisms, but in
theory it can be used to break the abstraction. However, given that you're
already giving people an escape route via the .Internal module, I don't
think that's as big a concern.

On Wed, Apr 22, 2015 at 11:04 AM Edward Z. Yang  wrote:
...
That's what I get for guessing syntax. Fixed.
Edward
Excerpts from Michael Snoyman's message of 2015-04-22 08:54:32 +0100:
...
Small request: could you bump the upper bound to allow base 4? ;)
On Wed, Apr 22, 2015 at 10:50 AM Edward Z. Yang  wrote:
...
Hello all,
Taking the appropriate suggestion, I have created a small
package to provide this functionality:
https://hackage.haskell.org/package/nf
If it migrates into deepseq, we can update this package to reexport
the appropriate modules from deepseq when it is available.
Please let me know if there's anything (e.g. version bounds) which
I can do to make this more "enterprise" ready.
Cheers,
Edward
Excerpts from Edward Z. Yang's message of 2015-02-10 08:46:37 +0000:
...
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

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