[mercury-users] errors with typeclasses

[david wallin]

>
>The fix is straight-forward:
>
>  	:- func list_add_chromosome(list_population,
>  			    C) = list_population <= chromosome(C).
>  	:- mode list_add_chromosome(in, in) = out is det.
>
>  	list_add_chromosome(PopIn, Chromosome) = PopOut :-
>  		PopIn = list_population(List),
>  		PopOut = list_population([some_chromosome(Chromosome) | List]).
>
>Likewise for the other methods.
>

Ok, I did that (but changed the variable name to C1 for clarity). 
This error seems strange to me (surprise!) since the 
'some_chromosome' type declaration constrains C to implement the 
chromosome typeclass, what's the problem ?

gusga.m:101: In clause for function `gusga:list_add_chromosome/2':
gusga.m:101:   in argument 1 of functor `list_population/1':
gusga.m:101:   in argument 1 of functor `./2':
gusga.m:101:   in unification of argument
gusga.m:101:   and term `some_chromosome(Chromosome)':
gusga.m:101:   type error in argument(s) of functor `some_chromosome/1'.
gusga.m:101:   Argument 1 (Chromosome) has type `C1',
gusga.m:101:   expected type was `C'.



--david.


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