[mercury-users] higher order types + type class constraints

[Michael Day]

How does one pass around higher order terms that have type class
constraints?

This is not correct:

:- pred foo(pred(C, C) <= something(C), other args ...).
:- mode foo(pred(di, uo) is det, other args ...) is det.

While this compiles, but doesn't work:

:- pred foo(pred(C, C), other args ...) <= something(C).
:- mode foo(pred(di, uo) is det, other args ...) is det.

foo(P, others ...) :-
	create C0,
	P(C0, C)		% error here, expects type to be `C'

Any suggestions? Which section of the reference manual should have this,
higher order section or type class constraints section?

Michael

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