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Control

Built-ins and language constructs to control execution

Predicates

!
Cut - succeeds and removes all choice points between cut and parent goal.
+Condition *-> +Then ; +Else
Soft-cut-conditional construct - succeeds if Then succeeds for some solution of Condition, or if Condition fails and Else succeeds
+Goal1 , +Goal2
Comma (AND) operator - succeeds if the goals Goal1 and Goal2 both succeed
+Condition -> +Then ; +Else
Conditional construct - succeeds if Then succeeds for the first solution of Condition, or if Condition fails and Else succeeds.
-?-> ?Body
The matching operator. The head of the clause which contains it will not be unified with the caller, one-way matching will be used instead.
+LookupModule : +Goal
Call the procedure visible in LookupModule rather than the caller module
+Goal1 ; +Goal2
Semicolon (OR) operator - Succeeds if the goal Goal1 succeeds or if the goal Goal2 succeeds.
Goal @ ContextModule
Goal is executed in the calling context of ContextModule.
\+ +Goal
Succeeds if Goal cannot be satisfied. Uses negation as failure (synonym of not/1).
+Vars ^ +Goal
Succeeds if Goal succeeds.
abort
The current computation is aborted and control is returned to the top level.
call(+Goal)
Succeeds if Goal succeeds.
call(+GoalPrefix, ?Arg, ?...)
Call with any number of additional arguments
catch(+Goal, ?Catcher, +Recovery)
Equivalent to call(Goal) if Goal succeeds or fails. If Goal throws an exception that unifies with Catcher, Recovery is executed
+IterationSpecs do +Goals
Execute Goals iteratively according to IterationSpecs.
fail
Does not succeed. A synonym of false/0.
false
Does not succeed (synonym of fail/0).
fork(+Max, -I)
Succeeds for all integers I between 1 and Max. The solutions are generated in parallel.
not +Goal
Succeeds if Goal cannot be satisfied (uses negation as failure).
once +Goal
Succeeds if Goal succeeds, and removes all its alternatives --- equivalent to call((Goal, !))
phrase(+Grammar, ?List)
Succeeds if List unifies with a list from the specified grammar Grammar.
phrase(+Grammar, ?Tokens, ?Remainder)
Succeeds if Tokens can be parsed as part of the grammar defined in Grammar and Remainder contains any remaining terms in Tokens.
repeat
Succeeds as often as tried.
throw(+Ball)
Throw an exception described by Ball. Continue execution at the recovery procedure of a matching ancestor catch/3
true
Succeeds always.
~ +Goal
The sound negation operator. If Goal is not ground, the predicate delays.

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