[m-users.] Anonymous recursive functions/predicates

[Mark Clements (gmail)]

In the process of translating some old SML code to Mercury, I was unable 
to translate for an anonymous recursive function. Such 
functions/predicates are useful for quickly rolling loops. Is there any 
way to declare or use an anonymous recursive function in Mercury?

As a simple example which counts the number of predicates that are true 
in a range (and which could be written in a number of other ways:):

:- func count2(func(int) = bool, int, int) = int.
count2(Predicate, Start, Finish) = Result :-
     %% Loop is an anonymous function that tries to call itself
     Loop = (func(I, Y) = (if I>Finish then Y
                           else Loop(I+1, if Predicate(I)=yes then Y+1 
else Y))),
     Result = Loop(Start, 0).

As an example of this function being called:

count2(func(I) = (if I>5 then yes else no), 0, 10)

but this gives an error:

:   In clause for `count2(in, in, in) = out':
:   mode error: variable `Loop' has instantiatedness
:   `free',
:   expected instantiatedness for non-local variables
:   of lambda goals is `ground'.
:
:   In clause for `count2(in, in, in) = out':
:   in argument 1 (i.e. the function term) of
:   higher-order function call:
:   mode error: variable `Loop' has instantiatedness
:   `free',
:   expecting higher-order func inst of arity 2.

Any guidance here would be appreciated.

Sincerely, Mark.