Control

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 context 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.