Supported Predicates and Functions in PAL

PAL Predicates

PAL supports mostly predicates that test the properties of frame arguments; PAL also includes a limited number of arithmetic and string predicates, plus miscellaneous predicates.

In addition, any slot of a knowledge base can be used as a unary predicate, the first argument being the class to which the slot is attached and the second argument being a slot value (see example).

Note on the strategy for evaluating predicates:

• Evaluation is lazy
• Evaluation is entire­the domain of predicates is the entire universe
• Inappropriate arguments are simply false
• There is no such thing as a list. Iteration is a procedural concept which maps to either forall or exists

Frame-system predicates

Frame-level predicates

• is-frame (1 argument: any type)

Class-level predicates

• direct-subclass-of (2 arguments: the subclass and the superclass)
• direct-superclass-of (2 arguments: the superclass and the subclass)
• is-class (1 argument: any type)
• is-concrete-class (1 argument: any type)
• subclass-of (2 arguments: the subclass and the superclass)
• superclass-of (2 arguments: the superclass and the subclass)

Slot-level predicates

• allowed-slot-value (3 arguments: slot, class that slot is attached to, a value)
• allowed-slot-value-type (3 arguments: slot, class that slot is attached to, class which defines value type)
• direct-template-slot-of (2 arguments: a slot and a class)
• own-slot-has-duplicate-values (2 arguments: a slot and a frame)
• own-slot-not-null (2 arguments: a slot and a frame)
• own-slot-of (2 arguments: a slot and a frame)
• slot-at-class-is-boolean-valued (2 arguments: a slot and a class)
• slot-at-class-is-class-valued (2 arguments: a slot and a class)
• slot-at-class-is-float-valued (2 arguments: a slot and a class)
• slot-at-class-is-frame-valued (2 arguments: a slot and a class)
• slot-at-class-is-instance-valued (2 arguments: a slot and a class)
• slot-at-class-is-integer-valued (2 arguments: a slot and a class)
• slot-at-class-is-primitive-valued (2 arguments: a slot and a class)
• slot-at-class-is-single-valued (2 arguments: a slot and a class)
• slot-at-class-is-string-valued (2 arguments: a slot and a class)
• slot-at-class-is-symbol-valued (2 arguments: a slot and a class)
• slot-has-duplicate-values (2 arguments: a slot and a frame)
• slot-is-boolean-valued (1 argument: the slot in question)
• slot-is-class-valued (1 argument: the slot in question)
• slot-is-float-valued (1 argument: the slot in question)
• slot-is-frame-valued (1 argument: the slot in question)
• slot-is-instance-valued (1 argument: the slot in question)
• slot-is-integer-valued (1 argument: the slot in question)
• slot-is-primitive-valued (1 argument: the slot in question)
• slot-is-single-valued (1 argument: the slot in question)
• slot-is-string-valued(1 argument: the slot in question)
• slot-is-symbol-valued (1 argument: the slot in question)
• slot-not-null (2 arguments: a slot and a frame)
• slot-of (2 arguments: a slot and a frame)
• template-slot-has-duplicate-values (2 arguments: a slot and a frame)
• template-slot-not-null (2 arguments: a slot and a class)
• template-slot-of (2 arguments: a slot and a class)

Facet-level predicates

• facet-not-null (3 arguments: a facet, a frame, and a slot)
• own-facet-not-null (3 arguments: a facet, a frame, and a slot)
• template-facet-not-null (3 arguments: a facet, a class, and a slot)

Instance-level predicates

• direct-instance-of (2 arguments: a frame and a class)
• instance-of (2 arguments: a frame and a class)

Arithmetic predicates

• even (1 argument: an integer)
• negative (1 argument: a number)
• odd (1 argument: an integer)
• positive (1 argument: a number)
• prime (1 argument: an integer)
• < (2 arguments, both numbers)
• > (2 arguments, both numbers)
• zero

String predicates

• prefix-of (2 arguments: the smaller string and the larger string)
• substring-of (2 arguments: the smaller string and the larger string)
• suffix-of (2 arguments: the smaller string and the larger string)

Miscellaneous predicates

• element-of (2 arguments, currently broken)

PAL Functions

PAL supports functions that test argument frames, as well as type-coercion functions and a few arithmetic functions.

In addition, any slot of a knowledge base can be used as a function, the only argument being the class to which the slot is attached, and the return type being the value-type of the slot (see example).

Note on the strategy for evaluating predicates:

• Evaluation is lazy
• Validation is entirely on number of arguments
• Types are cast, not coerced
• Type checking is, in general, impossible

Frame-system functions

• get-class  (1 argument: a frame. Return type is class.)
• number-of-own-slot-values (2 arguments: a slot and a frame. Return type is integer.)
• number-of-slot-values (2 arguments: a slot and a frame. Return type is integer.)
• number-of-template-slot-values (2 arguments: a slot and a frame. Return type is integer)

Coercion  functions

• coerce-to-class (1 argument: anything will do. Return type is class.)
• coerce-to-facet (1 argument: anything will do. Return type is facet.)
• coerce-to-frame (1 argument: anything will do. Return type is frame.)
• coerce-to-instance (1 argument: anything will do. Return type is instance.)
• coerce-to-integer (1 argument: anything will do. Return type is integer.)
• coerce-to-number (1 argument: anything will do. Return type is number.)
• coerce-to-slot (1 argument: anything will do. Return type is slot.)
• coerce-to-string (1 argument: anything will do. Return type is string.)
• coerce-to-symbol (1 argument: anything will do. Return type is symbol.)

Arithmetic functions

• + (2 arguments: both numbers. Return type is number.)
• - (2 arguments: both numbers. Return type is number.)
• * (2 arguments: both numbers. Return type is number.)
• / (2 arguments: both numbers. Return type is number.)
• round (1 arguments: a number. Return type is integer.)
• truncate (1 arguments: a number. Return type is integer.)

Extending PAL with additional predicates and functions.