uire a nominal parameter, the newtype would expect a
>>> representational coercion, not the nominal one you are passing. Check the
>>> dump (using -ddump-tc) of the newtype axiom to be sure.
>>>
>>> Though putting a `Sub` on `` and changing the Refl constructor on
>
o tc ...` over `AppCo (Refl
>> (TyConApp tc [])) ...`.
>>
>> In sum, here is the coercion I think you want:
>>
>> (LambdaCCC.Lambda.EP (Sym (Simple.NTCo:HasIf[0] _R)))_R
>>
>> This is one of the problems with roles -- they are *very* fiddly within GHC,
>>
ple.NTCo:HasIf[0] _R)))_R
>>
>> This is one of the problems with roles -- they are *very* fiddly within
>> GHC, and it's hard for a non-expert in roles to get them right.
>>
>> Have you seen docs/core-spec/core-spec.pdf? That is updated w.r.t. roles
>> and m
t. roles and
> may be of help.
>
> Let me know if I can help further!
> Richard
>
> On Apr 14, 2014, at 5:45 AM, Simon Peyton Jones wrote:
>
>> I think you need a ‘Sub’.
>>
>> A cast (e `cast` g) requires a representational coercion. I think you have
>&
t;
> A cast (e `cast` g) requires a representational coercion. I think you
> have given it a (stronger) nominal one. Sub gets from one to t’other.
>
> Simon
>
> *From:* Glasgow-haskell-users [mailto:glasgow-
> haskell-users-boun...@haskell.org] *On Behalf Of *Conal Elliott
> *
-users
> [mailto:glasgow-haskell-users-boun...@haskell.org] On Behalf Of Conal Elliott
> Sent: 14 April 2014 06:00
> To: ghc-devs@haskell.org; glasgow-haskell-us...@haskell.org
> Subject: Help with coercion & roles?
>
> I’m working on a GHC plugin (as part of my Haskell-to-hard
April 2014 06:00
To: ghc-devs@haskell.org; glasgow-haskell-us...@haskell.org
Subject: Help with coercion & roles?
I’m working on a GHC plugin (as part of my Haskell-to-hardware work) and
running into trouble with coercions & roles. Error message from Core Lint:
Warning: In the ex
I’m working on a GHC plugin (as part of my Haskell-to-hardware work) and
running into trouble with coercions & roles. Error message from Core Lint:
Warning: In the expression:
LambdaCCC.Lambda.lamvP#
@ (GHC.Types.Bool → GHC.Types.Bool → GHC.Types.Bool → GHC.Types.Bool)
@ (Simple.HasIf G
