It looks like this instance is partial. Note that the record field 'y' is also a partial function in plain Haskell. I've always considered this a misfeature, but perhaps fixing that is outside the scope of this proposal.
Erik On Mon, Jun 24, 2013 at 4:40 PM, Oliver Charles <ol...@ocharles.org.uk> wrote: > On 06/24/2013 08:44 AM, Adam Gundry wrote: >> Hi everyone, >> >> I am implementing an overloaded record fields extension for GHC as a >> GSoC project. Thanks to all those who gave their feedback on the >> original proposal! I've started to document the plan on the GHC wiki: >> >> http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/Plan >> >> If you have any comments on the proposed changes, or anything is unclear >> about the design, I'd like to hear from you. >> >> Thanks, >> >> Adam Gundry >> >> _______________________________________________ >> Glasgow-haskell-users mailing list >> Glasgow-haskell-users@haskell.org >> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > The wiki page says: > > The base design has the following distinct components: > > * A library class > > class Has (r :: *) (f :: String) (t :: *) where > get :: r -> t > > * A record declaration generates an instance declaration for each > field. For example > > data T a = T1 { x :: a, y :: Bool } > | T2 { x :: a } > > would generate > > instance (t~a) => Has (T a) "x" t where > get (T1 x _) = x > get (T2 x) = x > instance (t~Bool) => Has (T a) "y" t where > get (T1 _ y) = y > > Is this instance for "y" not partial? If it is, is that a problem? > Perhaps I missed something that makes that instance total. > > - Ollie > > > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
