booleans.pl

:- module(booleans, [and/2, or/2]).

:- op(1000, xfy, and).
:- op(1000, xfy, or).

and(P, Q) :- P , Q.

or(P, Q) :- P ; Q.

error.sh

➜  prolog  swipl 
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 6.2.6)
Copyright (c) 1990-2012 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- [booleans].
% booleans compiled into booleans 0.00 sec, 3 clauses
true.

?- true and false.
ERROR: Syntax error: Operator expected
ERROR: true 
ERROR: ** here **
ERROR: and false .