Afaik, you couldn't UNPACK a list in the past because it's a sum type, and sum types could not be unpacked. That has changed with the latest GHC, so maybe that now works. I'm pretty certain you can't unpack polymorphic fields, and this is why libraries such as `ad` offer a polymorphic version, and a version specialized to a particular type: http://hackage.haskell.org/package/ad-4.3.3/docs/Numeric-AD-Mode-Forward.htm... - polymorphic http://hackage.haskell.org/package/ad-4.3.3/docs/Numeric-AD-Mode-Forward-Dou... - specialized to Double and significantly faster Does that help? On Fri, Jul 28, 2017 at 2:48 PM Tom Ellis < tom-lists-haskell-cafe-2013@jaguarpaw.co.uk> wrote:
What types can be UNPACK'ed? From my vague understanding of what UNPACK does, it can only be types whose size is bounded by a known value, so whilst
data Foo = Foo {-# UNPACK #-} !Float {-# UNPACK #-} !Int
is fine, presumably
data Foo = Foo {-# UNPACK #-} ![Float]
is not fine. Or is it? Technically it could be possible to reserve enough space in Foo to store either a [] or a (:) Float [Float]. And if that is possible could we also UNPACK polymorphic fields?
data Storable a => Foo a = Foo {-# UNPACK #-} a
or
data Foo a where Foo :: Storable a => {-# UNPACK #-} a -> Foo a
if either DatatypeContexts worked or my imaginary GADT UNPACK syntax worked (I'm not sure if either does).
What are the limits of what we could reasonably get to UNPACK in GHC?
Thanks,
Tom _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.