Control constructs/predicates

Author(s): Daniel Cabeza, Manuel Hermenegildo.

Version: 1.5#118 (2000/4/19, 18:13:43 CEST)

Version of last change: 1.5#66 (2000/3/16, 17:3:30 CET)

This module contains the set of basic control predicates, except the predicates dealing with exceptions, which are in section Exception handling.

• Usage and interface (basiccontrol)
• Documentation on exports (basiccontrol)
• Documentation on internals (basiccontrol)

Usage and interface (basiccontrol)

Documentation on exports (basiccontrol)

PREDICATE: ,/2:

P , Q

Conjunction (P and Q).

Usage 2: * ISO *

• The following properties should hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) Q is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PREDICATE: ;/2:

P ; Q

Disjunction (P or Q).

Usage 2: * ISO *

• The following properties should hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) Q is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PREDICATE: ->/2:

P -> Q

If P then Q else fail, using first solution of P only. Also, (P -> Q ; R), if P then Q else R, using first solution of P only. No cuts are allowed in P.

Usage 2: * ISO *

• The following properties should hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) Q is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PREDICATE: !/0:

Usage 1: * ISO *

• Description: Commit to any choices taken in the current predicate.

Usage 2: * ISO *

• Description: Commit to any choices taken in the current predicate.

PREDICATE: \+/1:

\+ P

Goal P is not provable (negation by failure). Fails if P has a solution, and succeeds otherwise. No cuts are allowed in P.

Usage 2: * ISO *

• The following properties should hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PREDICATE: if/3:

if(P,Q,R)

If P then Q else R, exploring all solutions of P. No cuts are allowed in P.

Usage 2:

• The following properties should hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) Q is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) R is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PREDICATE: true/0:

Usage 1: * ISO *

• Description: Succeed (noop).

Usage 2: * ISO *

• Description: Succeed (noop).

PREDICATE: fail/0:

Usage 1: * ISO *

• Description: Fail, backtrack immediately.

Usage 2: * ISO *

• Description: Fail, backtrack immediately.

PREDICATE: repeat/0:

Usage 1: * ISO *

• Description: Generates an infinite sequence of backtracking choices.

Usage 2: * ISO *

• Description: Generates an infinite sequence of backtracking choices.

PREDICATE: call/1:

call(G)

Executes goal G, restricting the scope of the cuts to the execution of G. Writing a variable G in a goal position is equivalent.

Meta-predicate with arguments: call(goal).

Usage 2: * ISO *

• The following properties should hold at call time: G is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

Documentation on internals (basiccontrol)

PREDICATE: |/2:

An alias for disjunction (when appearing outside a list). The alias is performed when terms are read in.

PREDICATE: call/2:

call(Pred,Arg1)

There exists a set of builtin predicates of the form call/N such that execute predicate Pred given arguments Arg1 ... ArgX, if Pred has already arguments the new ones are added to the start. This predicate can be written using the special Ciao syntax Pred(Arg1,...,ArgX).

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