Notwithstanding the visibility rules, any predicate can be called from any other module by prefixing the goal with the module name and the colon operator, thus overriding the source module of the goal:
| ?- foo:bar(X).
This feature is intended mainly for debugging purposes, since it defies the purposes of the module system. If the prefixed goal is a meta-predicate, however, the prefixed module name may affect the module name expansion of the goal (see Meta Exp). If multiple module prefixes are used, the innermost one has priority.
It is also possible to override the source module of clauses and directives by module prefixing. For example,
:- dynamic mod:p/1. p(X) :- mod:(q(X), r(X)). mod:(q(X) :- r(X)). mod:s(X) :- t(X).
mod:p/1 as dynamic, whatever the source
module is; defines
p/1 in the source module as calling
mod:q/1 as calling
mod:r/1; and defines
mod:s/1 as calling
t/1 in the
source module. The latter technique is particularly useful when
the prefix is
user and the predicate is a hook
predicate such as
user:portray/1, which must be defined in the
user module, but the rest of the file consists of
predicates belonging to some other module.