[mercury-users] Seemingly spurious 'some but not all arguments have modes' error.

[Julian Fondren]

This error:

  partialmode.m:026: Error: some but not all arguments have modes:
command((string :: in), out(pred((list(dummy) :: in), (io :: di), (io
:: uo)) is det)).
  partialmode.m:027: Error: clause for predicate `partialmode.command/2'
  partialmode.m:027:   without preceding `pred' declaration.
  partialmode.m:027: Inferred :- pred command(string,
pred((list.list((partialmode.dummy))), (io.state), (io.state))).
  partialmode.m:027: Error: no mode declaration for predicate
  partialmode.m:027:   `partialmode.command/2'.
  partialmode.m:027:   (Use `--infer-modes' to enable mode inference.)
  partialmode.m:027: Inferred :- mode command(in, out(/* unique */(pred((ground
  partialmode.m:027:   >> ground), (unique >> clobbered), (free >> unique)) is
  partialmode.m:027:   det))).

comes from the trailing module.  Using the commented pred/mode
declarations, it compiles and operates without remark.  The
first line of the error message seems really strange, in that
it shows nicely moded arguments.

Cheers,
Julian


:- module partialmode.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module bool, list, string, require.

:- type dummy
        ---> dummy(
                name :: string,
                is_mortal :: bool
        ).

main(!IO) :-
        Args = ["dump"],
        (
                command(list.head(Args), Command)
        ->
                Command([dummy("socrates", yes),dummy("plato", yes)], !IO)
        ;
                error("inconceivable!")
        ).

:- pred command(string, (pred(list(dummy), io, io))).
:- mode command(in, out(pred(in, di, uo) is det)) is semidet.
% :- pred command(string::in, out(pred(list(dummy)::in, io::di,
io::uo) is det)) is semidet.
command("dump", dump).

:- pred dump(list(dummy)::in, io::di, io::uo) is det.
dump([], !IO).
dump([H | T], !IO) :-
        io.format("%s - %s\n", [s(H^name), s(to_string(H^is_mortal))], !IO),
        dump(T, !IO).

:- func to_string(bool) = string.
to_string(yes) = "yes".
to_string(no) = "no".
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