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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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− | *The special form '''define-type''' has several options
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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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− | *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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− | *Field attributes:
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− | **'''read-only:''' non mutable field
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− | **'''equality-skip:''' the '''equal?''' function will ignore this field
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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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