[m-dev.] taking addresses of multi-moded predicates

[Peter Wang]

Hi,

I think the majority of cases where you *really* want to take the
address of a predicate with multiple modes fall into this sort of pattern:

    mymap(P, L0, L) :-
	map(wrap(P), L0, L).

    :- pred wrap(...).
    :- mode wrap(in(pred(...) is det), ...) is det.
    :- mode wrap(in(pred(...) is cc_multi, ...) is cc_multi.
    ...

i.e. wrappers around other higher order predicates.  Explicit lambdas
don't cut it in this case as you need to write mode-specific versions of
the wrapper predicate, and perhaps its callers and so on.

Observations:

- when taking the address of a multi-moded predicate, there will most
  likely be one or more higher-order curried arguments provided

- we should (will?) know the insts of those arguments

- at the point where the higher order term is constructed, it will
  nearly always be possible to select the mode of the predicate by
  only matching the insts of the higher order curried arguments against
  the predicate's declared modes

I think that will provide 90% of the benefit with 1% of the effort
needed for the full solution.

Have I missed something?

Peter

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