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86 lines
4.0 KiB
Racket
86 lines
4.0 KiB
Racket
#lang racket/base
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(require (for-syntax racket/base syntax/parse racket/syntax syntax/datum syntax/strip-context))
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(provide (all-defined-out))
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;; a little tricky because we have to mix two levels of macrology.
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(define-syntax (br:debug-define stx)
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(syntax-parse stx
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#:literals (syntax)
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[(_ (syntax (id pat-arg ... . rest-arg)) body-exp) ; (define #'(foo arg) #'(+ arg arg))
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#'(define-syntax id (λ (stx)
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(define result (syntax-case stx ()
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[(_ pat-arg ... . rest-arg)
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body-exp]))
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(define arg-printing (syntax-case stx ()
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[(_ pat-arg ... . rest-arg)
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#`(begin
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(displayln (format "arg #'~a = ~a" #,''pat-arg pat-arg)) ...)]))
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(with-syntax ([syntaxed-arg-printing arg-printing]
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[syntaxed-result result])
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#'(begin
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(displayln (format "input syntax = #'~a" (quote (id pat-arg ... . rest-arg))))
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(displayln (format "output syntax = #'~a" (syntax->datum body-exp)))
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syntaxed-arg-printing
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(displayln (format "expanded syntax = #'~a" 'syntaxed-result))
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syntaxed-result))))]))
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(module+ test
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(require rackunit racket/port)
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(check-equal? (parameterize ([current-output-port (open-output-nowhere)])
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(br:debug-define #'(foo <x> <y> <z>)
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#'(apply + (list <x> <y> <z>)))
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(foo 1 2 3)) 6))
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;; does not work with ellipses in the input pattern
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#;(br:debug-define #'(foo <x> ...)
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#'(apply + (list <x> ...)))
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(define-syntax (br:define stx)
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(define-syntax-class syntaxed-id
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#:literals (syntax)
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#:description "id in syntaxed form"
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(pattern (syntax name:id)))
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(syntax-parse stx
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#:literals (syntax)
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[(_ (syntax (id pat-arg ... . rest-arg)) body ...) ; (define #'(foo arg) #'(+ arg arg))
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#'(define-syntax id (λ (stx)
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(define result
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(syntax-case stx ()
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[(_ pat-arg ... . rest-arg) body ...]))
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(if (not (syntax? result))
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(datum->syntax stx result)
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result)))]
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[(_ sid:syntaxed-id sid2:syntaxed-id) ; (define #'f1 #'f2)
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#'(define-syntax sid.name (make-rename-transformer sid2))]
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[(_ (sid:syntaxed-id stx-arg ...) expr ...) ; (define (#'f1 stx) expr ...)
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(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))]
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[(_ sid:syntaxed-id (λ (stx-arg ...) expr ...)) ; (define #'f1 (λ(stx) expr ...)
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#:fail-when (not (= (length (syntax->datum #'(stx-arg ...))) 1))
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(raise-syntax-error 'define "did not get exactly one argument for macro" (syntax->datum #'(stx-arg ...)))
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#'(define-syntax (sid.name stx-arg ...) expr ...)]
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[(_ args ...) #'(define args ...)]))
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(module+ test
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(require rackunit)
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(br:define #'plus (λ(stx) #'+))
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(br:define #'plusser #'plus)
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(br:define #'(times arg) #'(* arg arg))
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(br:define #'timeser #'times)
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(check-equal? (plus 42) +)
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(check-equal? plusser +)
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(check-equal? (plusser 42) +)
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(check-equal? (times 10) 100)
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(check-equal? (timeser 12) 144)
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(check-equal? (let ()
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(br:define #'(foo x)
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(with-syntax ([zam +])
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#'(zam x x))) (foo 42)) 84)
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;; todo: error from define not trapped by check-exn
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#;(check-exn exn:fail:syntax? (λ _ (br:define (#'times stx stx2) #'*))))
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