Re: [jhc] A possible bug with constraints being perceived as multiparameter type classes

On 21/04/15 17:09, Roman Cheplyaka wrote:

On 21/04/15 16:38, Brandon Allbery wrote:

...

On Tue, Apr 21, 2015 at 9:26 AM, Artyom mailto:yom@artyom.me> wrote:

|$ Temp/jhc-0.8.2/jhc Temp/jhc1.hs

jhc Temp/jhc1.hs jhc 0.8.2 (mydniquipepo-32) Finding Dependencies... Using Ho Cache: '/home/yom/.jhc/cache'

Temp/jhc1.hs:1 - Error: Invalid Class. multiparameter classes not yet supported: (Num,[HsTyTuple [HsTyVar {hsTypeName = a},HsTyVar {hsTypeName = b}]]) |

Am I misunderstanding something, or is it a legitimate bug?

​

Looks multiparameter to me:

instance ... => Num (T a b Int) where

with T ~ (,,). Which is what the second line of the error message is telling you, more or less.

No, it's a multi-parameter type, but a single-parameter class.

Multi-parameter would be Num a b Int.

Roman

That said, it's not H98 either (ghc would require FlexibleInstances), so jhc may be right in rejecting in, just not explaining it properly. Roman