Vocabulary
syntax

Syntax

PREDICATE: class < superclass predicate... ;

Inputs and outputs

class	a new class word to define
superclass	an existing class word
predicate	membership test with stack effect ( superclass -- ? )

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 ;