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- | == define-type / define-structure usage ==
| + | #REDIRECT [[Documentation:Special_form_define-record-type]] |
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- | Here is a traduction of some of Marc's slides from an introduction to scheme course. I believe they might be usefull since define-type / define-record are very lightly documented in the official doc.
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- | | + | |
- | === Syntax ===
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- | | + | |
- | (define-type type-name <attribute or field>...)
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- | Attribute is a keyword. An attribute may have arguments?
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- | Field is a symbol or a list. If a list, the first element is the field name, optionally followed by getter and setter, then field attributes
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- | | + | |
- | The simplest form of syntax specifies only the type name and the name of each fields
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- | *ex:
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- | | + | |
- | :C: '''typedef struct { int x; int y; } point2d;'''
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- | :Gambit : '''(define-type point2d x y)'''
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- | | + | |
- | *Such type definition are equivalent to multiple definitions:
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- | (define (make-point2d x y)...) ;constructor
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- | (define (point2d? obj)... ) ;predicate
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- | (define (point2d-x p)...) ;access to x field
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- | (define (point2d-x-set! p x)...) ;mutation of x field
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- | (define (point2d-y p)...) ;access to y field
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- | (define (point2d-y-set! p y)...) ;mutation of y field
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- | | + | |
- | *ex:
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- | | + | |
- | > (define-type point2d x y)
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- | > (define p (make-point2d 11 22))
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- | > p
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- | #<point2d #2 x: 11 y: 22>
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- | > (point2d? p)
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- | #t
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- | > (point2d-x p)
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- | 11
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- | > (point2d-x-set! p 33)
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- | > p
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- | #<point2d #2 x: 33 y: 22>
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- | | + | |
- | === define-type attributes ===
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- | | + | |
- | *These structures also supports inheritance
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- | *The parameter '''extender:''' ''name'' specifies the name of the definition form to use to define a subtype:
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- | > (define-type point2d
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- | extender: define-type-of-point2d
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- | x
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- | y)
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- | > (define-type-of-point2d point3d z)
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- | > (define p3 (make-point3d 11 22 33))
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- | > p3
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- | #<point3d #2 x: 11 y: 22 z: 33>
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- | > (point2d? p3)
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- | #t
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- | > (point3d? p3)
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- | #t
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- | > (point2d-x p3)
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- | 11
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- | > (point3d-z p3)
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- | 33
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- | | + | |
- | | + | |
- | TODO other define-type's parameters:
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- | *'''id:'''
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- | *'''constructor:'''
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- | *'''constant-constructor:'''
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- | *'''predicate:'''
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- | *'''implementer:'''
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- | *'''type-exhibitor:'''
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- | *'''prefix:'''
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- | *'''opaque:'''
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- | *'''macros:'''
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- | | + | |
- | === Field attributes ===
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- | | + | |
- | *Field attributes:
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- | **'''read-write:'''
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- | **'''read-only:''' non mutable field
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- | **'''equality-test:'''
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- | **'''equality-skip:''' the '''equal?''' function will ignore this field
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- | **'''printable:'''
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- | **'''unprintable:''' the '''write''' function will ignore it
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- | **'''init:''' ''cst'' initial value
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- | | + | |
- | *ex:
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- | > (define-type noeud
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- | (a unprintable:)
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- | (b read-only: init: 9)
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- | (c equality-skip:))
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- | > (define x (make-noeud 1 2))
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- | > (noeud-a-set! x x)
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- | > x
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- | #<noeud #2 b: 9 c: 2>
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- | > (equal? x (make-noeud x 3))
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- | #t
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- | > (noeud-b-set! x 999)
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- | *** ERROR -- Unbound variable: noeud-b-set!
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- | | + | |
- | All field attributes except '''init:''' can be specified at define-type level and will affect all fields. A field can specify its own field attributes to override default attributes.
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- | | + | |
- | *ex:
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- | > (define-type foo unprintable: a (b printable:))
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- | > (make-foo 1 2)
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- | #<foo #3 b: 2>
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- | | + | |
- | *Field may have non-conventional getter and setter names, specified after field name in that order
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- | | + | |
- | *ex:
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- | > (define-type foo (a get-a) (b get-b set-b))
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- | > (define x (make-foo 1 2))
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- | > (get-a x)
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- | 1
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- | > (set-a x 2)
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- | *** ERROR IN (console)@14.2 -- Unbound variable: set-a
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- | > (get-b x)
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- | 2
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- | > (set-b x 3)
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- | > (get-b x)
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- | 3
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