An example of defining a mode for a type that only maintains partial uniqueness

inst_test.m

:- module inst_test.
:- interface.
% An example of defining a mode for a type that only maintains partial uniqueness.

% The type.
% In the inst, we will want to keep the string unique, but we won't worry about the int's uniqueness.
:- type test ---> test(int, string).

% Define the start and end states for the test_di mode.
:- inst test_in_di ---> test(ground, unique).
:- inst test_out_di ---> test(ground, clobbered).

% Define the start and end states for the test_uo mode.
:- inst test_in_uo ---> test(free, free).
:- inst test_out_uo ---> test(ground, unique).

% Define the test_di and test_uo modes.
:- mode test_di == test_in_di >> test_out_di.
:- mode test_uo == test_in_uo >> test_out_uo.

% A quick predicate that uses this mode.
:- pred str_test(test::test_di, test::test_uo) is det.

:- implementation.

:- import_module string.

% Int is not unique, but string.append makes unique strings.
str_test(test(Int, Str), test(Int, string.append(Str, "!"))).