Sorry to be slow
Simon
From: Alan & Kim Zimmerman [mailto:alan.z...@gmail.com]
Sent: 23 October 2017 22:36
To: Simon Peyton Jones <simo...@microsoft.com>
Cc: ghc-devs@haskell.org
Subject: Re: forall in constraint
In Shayan's implementation he has [1]
data ImplicitBndrs x thing
= IB
In Shayan's implementation he has [1]
data ImplicitBndrs x thing
= IB
(XIB x thing)
thing
| NewImplicitBndrs
(XNewImplicitBndrs x thing)
type family XIB x thing
type family XNewImplicitBndrs x thing
type ForallXImplicitBndrs c x thing =
( c (XIB
I’m lost. Could you give me a bit more context?
I’m deeply suspicious about that ForallXImplicitBndrs thing with strange higher
kinded parameters. Smells all wrong to me.
Simon
From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of Alan & Kim
Zimmerman
Sent: 23 October 2017 16:07
Hi Alan,
One way is to define a new typeclass.
type ImplicitBndrs c x thing
= (c (XIB x thing), c (XNewImplicitBndrs x thing))
class ForallImplicitBndrs c x where
withImplicitBndrs
:: forall thing. (ImplicitBndrs c x thing => t) -> t
Although that requires you to write one instance
