:- module f2.
:- interface.

:- import_module list.

:- type foo ---> foo(int).

:- typeclass cons(T) where [
    pred cons(T::in, list(string)::in, list(string)::out) is det
].

:- instance cons(foo).

:- implementation.

:- import_module string.

:- instance cons(foo) where [
    cons(foo(X), A, [S | A]) :-
        string.format("%d", [i(X)], S)
].

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