Templates
Description
abort aborts the current execution. If this execution was initiated under a top-level the control is given back to the top-level and the message {execution aborted} is displayed. Otherwise, e.g. execution started by a initialization/1 directive (section 6.1.13), abort/0 is equivalent to halt(1) (see below).
stop stops the current execution. If this execution was initiated under a top-level the control is given back to the top-level. Otherwise, stop/0 is equivalent to halt(0) (see below).
top_level starts a new recursive top-level (including the banner display). To end this new top-level simply type the end-of-file key sequence (Ctl-D) or its term representation: end_of_file.
break invokes a recursive top-level (no banner is displayed). To end this new level simply type the end-of-file key sequence (Ctl-D) or its term representation: end_of_file.
halt(Status) causes the GNU Prolog process to immediately exit back to the shell with the return code Status.
halt is equivalent to halt(0).
Errors
| Status is a variable | instantiation_error | |
| Status is neither a variable nor an integer | type_error(integer, Status) | |
Portability
halt/1 and halt/0 are ISO predicates. abort/0, stop/0, top_level/0 and break/0 are GNU Prolog predicates.
Templates
Description
once(Goal) succeeds if call(Goal) succeeds. However once/1 is not re-executable on backtracking since all alternatives of Goal are cut. once(Goal) is equivalent to call(Goal), !.
\+ Goal succeeds if call(Goal) fails and fails otherwise. This built-in predicate gives negation by failure.
call(Closure, Arg1,…, ArgN) calls the goal call(Goal) where Goal is constructed by appending Arg1,…, ArgN (1 ≤ N ≤ 10) additional arguments to the arguments (if any) of Closure.
call_with_args(Functor, Arg1,…, ArgN) calls the goal whose functor is Functor and whose arguments are Arg1,…, ArgN (0 ≤ N ≤ 10).
call_det(Goal, Deterministic) succeeds if call(Goal) succeeds and unifies Deterministic with true if Goal has not created any choice-points, with false otherwise.
\+ is a predefined prefix operator (section 7.14.10).
Errors
| Goal is a variable | instantiation_error | |
| Goal is neither a variable nor a callable term | type_error(callable, Goal) | |
| The predicate indicator Pred of Goal does not correspond to an existing procedure and the value of the unknown Prolog flag is error (section 7.22.1) | existence_error(procedure, Pred) | |
| Functor is a variable | instantiation_error | |
| Functor is neither a variable nor an atom | type_error(atom, Functor) | |
| Deterministic is neither a variable nor a boolean | type_error(boolean, Deterministic) | |
| for call/2-11 the resulting arity of Goal (arity of Closure + N) is an integer > max_arity flag (section 7.22.1) | representation_error(max_arity) | |
Portability
once/1 and (\+)/1 are ISO predicates, call/2-11, call_with_args/1-11 and call_det/2 are GNU Prolog predicates.
Templates
Description
repeat generates an infinite sequence of backtracking choices. The purpose is to repeatedly perform some action on elements which are somehow generated, e.g. by reading them from a stream, until some test becomes true. Repeat loops cannot contribute to the logic of the program. They are only meaningful if the action involves side-effects. The only reason for using repeat loops instead of a more natural tail-recursive formulation is efficiency: when the test fails back, the Prolog engine immediately reclaims any working storage consumed since the call to repeat/0.
Errors
None.
Portability
ISO predicate.
Templates
Description
for(Counter, Lower, Upper) generates an sequence of backtracking choices instantiating Counter to the values Lower, Lower+1,…, Upper.
Errors
| Counter is neither a variable nor an integer | type_error(integer, Counter) | |
| Lower is a variable | instantiation_error | |
| Lower is neither a variable nor an integer | type_error(integer, Lower) | |
| Upper is a variable | instantiation_error | |
| Upper is neither a variable nor an integer | type_error(integer, Upper) | |
Portability
GNU Prolog predicate.