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#lang racket/base
(require (for-syntax racket/base
racket/struct-info))
(provide make)
;; get-struct-info : identifier stx -> struct-info-list
(define-for-syntax (get-struct-info id ctx)
(define (bad-struct-name x)
(raise-syntax-error #f "expected struct name" ctx x))
(unless (identifier? id)
(bad-struct-name id))
(let ([value (syntax-local-value id (lambda () #f))])
(unless (struct-info? value)
(bad-struct-name id))
(extract-struct-info value)))
;; (make struct-name field-expr ...)
;; Checks that correct number of fields given.
(define-syntax (make stx)
(syntax-case stx ()
[(make S expr ...)
(let ()
(define info (get-struct-info #'S stx))
(define constructor (list-ref info 1))
(define accessors (list-ref info 3))
(unless (identifier? #'constructor)
(raise-syntax-error #f "constructor not available for struct" stx #'S))
(unless (andmap identifier? accessors)
(raise-syntax-error #f "incomplete info for struct type" stx #'S))
(let ([num-slots (length accessors)]
[num-provided (length (syntax->list #'(expr ...)))])
(unless (= num-provided num-slots)
(raise-syntax-error
#f
(format "wrong number of arguments for struct ~s (expected ~s, got ~s)"
(syntax-e #'S)
num-slots
num-provided)
stx)))
(with-syntax ([constructor constructor])
(syntax-property #'(constructor expr ...)
'disappeared-use
#'S)))]))
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