,/2 (comma)
Module: builtins
,/2 — conjunction of two goals
FORMS
FirstGoal, SecondGoal
DESCRIPTION
The first argument, FirstGoal, is called as a goal. If it succeeds, then the SecondGoal will be run. If either goal fails, the most recent alternative will be attempted after backtracking.
EXAMPLES
The following example shows the use of the ‘, ‘ connector :
?- listing.
lucky(mick,love).
boss(mick,jerri).
yes.
?- lucky(Who,What),boss(Who,Boss).
Who=mick
What=love
Boss=jerri
yes.
The goal submitted to the Prolog shell consists of two subgoals
-
lucky(Who, What) -
boss(Who, Boss)
The subgoals are connected together by using the ',' connective. In the next example, the first subgoal fails, so the second subgoal is not executed :
?- fail,write('Help, I am stuck in an example'),nl.
no.
The following shows that ‘, ‘ works the same in call/1 :
?- call((fail,write('Help, I am stuck in an example'),nl)).
no.
Note that the parentheses around the argument to call/1 are to keep the parser from creating a call to call/3.