[m-dev.] Typeclass problem

[Ralph Becket]

I want to define a type class like this:

	:- typeclass clausal(C, L) <= ((C -> L), literal(L)) where [

	    func clauses(C::ia) = (list(clause(L))::oa) is det

	].

but for

	:- instance clausal(clause(L), L)  <= literal(L).

the compiler is complaining that

clauses.m:053: Error: types in instance declarations must be functors
with distinct variables as arguments: clausal(clause(_1), _1).

Why is this restriction necessary when the second argument is a
function of the first?

-- Ralph
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