[m-users.] Field access functions usage

[Dirk Ziegemeyer]

Hi,

I’d like to use a field access function as a higher order term. As explained in reference manual section 3.4.1, I declare the function explicitly. This seems to affect the „normal“ field access syntax which does not compile any more.

Example:

:- type foo
    --->    foo(
                field_1 :: int,
                field_2 :: string
            ).


:- func field_1(foo) = int.


main(!IO) :-
    Foo = init_foo,
    _X = field_1(Foo),
    _Y = list.map(field_1, [Foo]).


:- func init_foo = foo.

init_foo = X :-
    X^field_1 = 5,
    X^field_2 = "bar".


Compiler error:
field_access_test.m:039: In clause for `init_foo = out':
field_access_test.m:039:   in argument 1 of call to function
field_access_test.m:039:   `field_access_test.field_1'/1:
field_access_test.m:039:   mode error: variable `X' has instantiatedness
field_access_test.m:039:   `unique(foo(free, unique("bar")))',
field_access_test.m:039:   expected instantiatedness was `ground’.

As soon as I add the declaration of the compiler-generated function field_1/1, init_foo/0 does not compile any more. What is wrong in my code?

Dirk.