[mercury-users] determinism not satisfied

[Terrence Brannon]

If anyone could help me get this simple program to work, I would
appreciate it. Program and compilation error messages follow.

% p.14 "Clause and Effect" by William Clocksin

:- module border.
:- interface.
:- import_module io.

:- pred main(io__state::di, io__state::uo) is det.

:- implementation.
:- import_module std_util.

main -->
	{ border("sussex",L) }, io__write_string(L).

border("sussex","kent").
border("sussex","surrey").

adjacent(X,Y) :- border(X,Y).
adjacent(X,Y) :- border(Y,X).

affordable(X,Y) :- adjacent(X,Z), adjacent(Z,Y).


[localhost:mercury/lexparse/border] metaperl% mmc --infer-all border.m
border.m:015: Inferred :- pred border(string, string).
border.m:018: Inferred :- pred adjacent(string, string).
border.m:021: Inferred :- pred affordable(string, string).
border.m:007: In `main(di, uo)':
border.m:007:   error: determinism declaration not satisfied.
border.m:007:   Declared `det', inferred `nondet'.
border.m:013:   call to `border(di, uo)' can fail.
border.m:013:   call to `border(di, uo)' can succeed more than once.
border.m:013: In clause for `main(di, uo)':
border.m:013:   in argument 2 of call to predicate `io:write_string/3':
border.m:013:   mode error: variable `DCG_0' has instantiatedness `mostly_unique',
border.m:013:   expected instantiatedness was `unique'.
border.m:015: Inferred :- mode border(di, uo) is nondet.
For more information, try recompiling with `-E'.
[localhost:mercury/lexparse/border] metaperl% 

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