1 USING: help.markup help.syntax kernel kernel.private
2 namespaces sequences words arrays effects math
3 classes.private classes.union classes.mixin
4 classes.predicate quotations ;
7 ARTICLE: "class-predicates" "Class predicate words"
8 "With a handful of exceptions, each class has a membership predicate word, named " { $snippet { $emphasis "class" } "?" } " . A quotation calling this predicate is stored in the " { $snippet "\"predicate\"" } " word property."
10 "When it comes to predicates, the exceptional classes are:"
12 { "Class" "Predicate" "Explanation" }
13 { { $link f } { $snippet "[ not ]" } { "The conventional name for a word which outputs true when given false is " { $link not } "; " { $snippet "f?" } " would be confusing." } }
14 { { $link object } { $snippet "[ drop t ]" } { "All objects are instances of " { $link object } } }
15 { { $link null } { $snippet "[ drop f ]" } { "No object is an instance of " { $link null } } }
17 "The set of class predicate words is a class:"
22 "A predicate word holds a reference to the class it is predicating over in the " { $snippet "\"predicating\"" } " word property." ;
24 ARTICLE: "classes" "Classes"
25 "Conceptually, a " { $snippet "class" } " is a set of objects whose members can be identified with a predicate, and on which generic words can specialize methods. Classes are organized into a general partial order, and an object may be an instance of more than one class."
27 "At the implementation level, a class is a word with certain word properties set."
29 "Words for working with classes are found in the " { $vocab-link "classes" } " vocabulary."
31 "Classes themselves form a class:"
32 { $subsections class? }
33 "You can ask an object for its class:"
34 { $subsections class }
35 "Testing if an object is an instance of a class:"
36 { $subsections instance? }
37 "You can ask a class for its superclass:"
43 "Class predicates can be used to test instances directly:"
44 { $subsections "class-predicates" }
45 "There is a universal class which all objects are an instance of, and an empty class with no instances:"
50 "Obtaining a list of all defined classes:"
51 { $subsections classes }
52 "There are several sorts of classes:"
61 { $link "tuples" } " are documented in their own section."
63 "Classes can be inspected and operated upon:"
68 { $see-also "class-index" } ;
73 { $values { "object" object } { "class" class } }
74 { $description "Outputs an object's canonical class. While an object may be an instance of more than one class, the canonical class is either its built-in class, or if the object is a tuple, its tuple class." }
75 { $class-description "The class of all class words." }
76 { $examples { $example "USING: classes prettyprint ;" "1.0 class ." "float" } { $example "USING: classes prettyprint ;" "IN: scratchpad" "TUPLE: point x y z ;\nT{ point f 1 2 3 } class ." "point" } } ;
79 { $values { "seq" "a sequence of class words" } }
80 { $description "Finds all class words in the dictionary." } ;
83 { $var-description "Assoc mapping each class to a set of classes defined in terms of this class. The " { $link define-class } " word uses this information to update generic words when classes are redefined." } ;
86 { $values { "word" "a word" } { "predicate" "a predicate word" } }
87 { $description "Suffixes the word's name with \"?\" and creates a word with that name in the same vocabulary as the word itself." } ;
89 HELP: define-predicate
90 { $values { "class" class } { "quot" quotation } }
91 { $description "Defines a predicate word for a class." }
95 { $values { "class" class } { "super" class } }
96 { $description "Outputs the superclass of a class. All instances of this class are also instances of the superclass." }
98 { $example "USING: classes prettyprint ;"
107 { "supers" sequence } }
108 { $description "Outputs a sequence of superclasses of a class along with the class itself." }
110 { $example "USING: classes prettyprint ;"
119 { "superclass" class }
122 { $description "Outputs a boolean value indicating whether " { $snippet "class" } " is at any level a subclass of " { $snippet "superclass" } "." }
124 { $example "USING: classes classes.tuple prettyprint words ;"
125 "tuple-class \\ class subclass-of? ."
130 { superclass superclasses subclass-of? } related-words
133 { $values { "class" class } { "seq" "a sequence of union members, or " { $link f } } }
134 { $description "If " { $snippet "class" } " is a union class, outputs a sequence of its member classes, otherwise outputs " { $link f } "." } ;
137 { $values { "class" class } { "seq" "a sequence of intersection participants, or " { $link f } } }
138 { $description "If " { $snippet "class" } " is an intersection class, outputs a sequence of its participant classes, otherwise outputs " { $link f } "." } ;
141 { $values { "word" word } { "superclass" class } { "members" "a sequence of class words" } { "participants" "a sequence of class words" } { "metaclass" class } }
142 { $description "Sets a property indicating this word is a class word, thus making it an instance of " { $link class } ", and registers it with " { $link update-map } "." }
146 { $values { "class/classes" "a class or a sequence of classes" } { "seq" "a sequence of generic words" } }
147 { $description "Finds all generic words in the dictionary implementing methods for the given set of classes." } ;
151 { "object" object } { "class" class }
152 { "?" "a boolean" } }
153 { $description "Tests whether the input object is a member of the class." } ;