PREDICATE:
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define-predicate-class ( class superclass definition -- )

Vocabulary
syntax

Syntax

PREDICATE: class < superclass predicate... ;

Inputs
None

Outputs
None

Word description
Defines a predicate class deriving from superclass.

An object is an instance of a predicate class if two conditions hold:

•	it is an instance of the predicate's superclass,
•	it satisfies the predicate

Each predicate must be defined as a subclass of some other class. This ensures that predicates inheriting from disjoint classes do not need to be exhaustively tested during method dispatch.

Examples

USING: math ; PREDICATE: positive < integer 0 > ;

See also
predicate-class, define-predicate-class

Definition

USING: classes.parser classes.predicate lexer parser ;

IN: syntax

SYNTAX: PREDICATE:
    scan-new-class "<" expect
    scan-class parse-definition define-predicate-class ;