Control

Predicates

!

Cut - succeeds and removes all choice points between cut and parent goal.

+Goal1 , +Goal2

Comma (AND) operator - succeeds if the goals Goal1 and Goal2 both succeed

+Condition -> +Then ; +Else

Conditional construct - succeeds if either Condition succeeds, and then Goal2 succeeds; or else if Condition fails, and then 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.

block(+Goal, ?Tag, +Recovery)

Similar to call(Goal) if Goal succeeds or fails. If an exit_block/1 is executed inside Goal, whose argument unifies with Tag, then Recovery is executed.

call(+Goal)

Succeeds if Goal succeeds.

+IterationSpecs do +Goals

Execute Goals iteratively according to IterationSpecs.

exit_block(++TagExit)

Continues the program at the recovery procedure of the block/3 predicate whose Tag argument unifies with TagExit.

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.

mutex(+MutexId, +Goal)

Equivalent to once(Goal) but with mutual exclusion among parallel workers.

mutex_init(+MutexId)

Initialise the mutual exclusion lock MutexId

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, ?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.

true

Succeeds always.

~?Goal

The sound negation operator. If Goal is not ground, the predicate delays.