[mercury-users] More on higher order functions

[Ralph Becket]

I'm experimenting with programming in the monadic
style in Mercury and I've discovered a mildly painful
hole in the default func mode assumption.

If I have

:- type stateT(S, A) ---> stateT(func(S) = pair(A, S)).

:- func stateT(S, A) `thenST` (func(A) = stateT(S, B)) = stateT(S, B).

and write

stateT(ST) `thenST` F =
	stateT((
		func(S0) = FX(S) :-
			(X-S) = ST(S0),
			stateT(FX) = F(X)
	)).

then I get all sorts of whinges from the compiler about
modes, the problem being that the default func mode
assumption doesn't extend to `wrapped up' functions.
My question is, would it be possible to extend the mode
assumption to ``wherever I know there's a function, and
no mode declarations have been made to the contrary, I
will assume that function has mode
`(in, ...) = out is det' ''?

Ralph
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