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beautiful-racket/br/define.rkt

48 lines
1.9 KiB
Racket

#lang racket/base
(require (for-syntax racket/base syntax/parse))
(provide (all-defined-out))
(define-syntax (br:define stx)
(define-syntax-class syntaxed-id
#:literals (syntax)
#:description "id in syntaxed form"
(pattern (syntax name:id)))
(syntax-parse stx
#:literals (syntax)
[(_ (syntax (id pat-arg ...)) body ...) ; (define #'(foo arg) #'(+ arg arg))
#'(define-syntax id (λ (stx)
(syntax-case stx ()
[(_ pat-arg ...) body ...])))]
[(_ sid:syntaxed-id sid2:syntaxed-id) ; (define #'f1 #'f2)
#'(define-syntax sid.name (make-rename-transformer sid2))]
[(_ (sid:syntaxed-id stx-arg ...) expr ...) ; (define (#'f1 stx) expr ...)
(raise-syntax-error 'define "definition of a syntax transformer must use lambda notation, because otherwise it's too easy to confuse the compile-time shape and the run-time shape" (syntax->datum #'sid.name))]
[(_ sid:syntaxed-id (λ (stx-arg ...) expr ...)) ; (define #'f1 (λ(stx) expr ...)
#:fail-when (not (= (length (syntax->datum #'(stx-arg ...))) 1))
(raise-syntax-error 'define "did not get exactly one argument for macro" (syntax->datum #'(stx-arg ...)))
#'(define-syntax (sid.name stx-arg ...) expr ...)]
[(_ args ...) #'(define args ...)]))
(module+ test
(require rackunit)
(br:define #'plus (λ(stx) #'+))
(br:define #'plusser #'plus)
(br:define #'(times arg) #'(* arg arg))
(br:define #'timeser #'times)
(check-equal? (plus 42) +)
(check-equal? plusser +)
(check-equal? (plusser 42) +)
(check-equal? (times 10) 100)
(check-equal? (timeser 12) 144)
(check-equal? (let ()
(br:define #'(foo x)
(with-syntax ([zam +])
#'(zam x x))) (foo 42)) 84)
;; todo: error from define not trapped by check-exn
#;(check-exn exn:fail:syntax? (λ _ (br:define (#'times stx stx2) #'*))))