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

[Roman Cheplyaka]

On 21/04/15 16:38, Brandon Allbery wrote:
> On Tue, Apr 21, 2015 at 9:26 AM, Artyom <yom at artyom.me
> <mailto:yom at 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