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
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
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