[m-rev.] for review: use typeclass constraints to help resolve overloading

[Peter Ross]

On Wed, Jan 16, 2002 at 03:15:36PM +1100, Peter Ross wrote:
> +:- pred instance_decl_exists(module_info::in, (type)::in,
> +		{int, class_constraint}::in) is semidet.
> +
> +instance_decl_exists(ModuleInfo, ArgType, {N, constraint(Name, Types)}) :-
> +	module_info_instances(ModuleInfo, Instances),
> +	map__lookup(Instances, class_id(Name, list__length(Types)),
> +			InstanceDefns),
> +	list__filter((pred(InstanceDefn::in) is semidet :-
> +			InstanceDefn = hlds_instance_defn(_, _, _, _,
> +					InstanceTypes, _, _, _, _),
> +			list__index1_det(InstanceTypes, N, InstanceType),
> +			type_list_subsumes([ArgType], [InstanceType], _)
> +		), InstanceDefns, Compatible, _Incompatible),
> +
> +		% There must be at least one instance declaration which
> +		% metions the ArgType.
> +	Compatible = [_ | _].

The arguments of type_list_subsumes are the wrong way around.
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