28 lines
1.0 KiB
Scheme
28 lines
1.0 KiB
Scheme
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(define-syntax record-case
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(lambda (x)
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(import scheme)
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(define (enumerate fld* i)
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(syntax-case fld* ()
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[() #'()]
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[(x . x*)
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(with-syntax ([i i] [i* (enumerate #'x* (add1 i))])
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#'(i . i*))]))
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(define (generate-body ctxt cls*)
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(syntax-case cls* (else)
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[() (with-syntax ([x x]) #'(error #f "unmatched ~s in ~s" v #'x))]
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[([else b b* ...]) #'(begin b b* ...)]
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[([(rec-name rec-field* ...) b b* ...] . rest) (identifier? #'rec-name)
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(with-syntax ([altern (generate-body ctxt #'rest)]
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[(id* ...) (enumerate #'(rec-field* ...) 0)]
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[rtd #'(type-descriptor rec-name)])
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#'(if ((record-predicate rtd) v)
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(let ([rec-field*
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((record-field-accessor rtd id*) v)] ...)
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b b* ...)
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altern))]))
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(syntax-case x ()
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[(_ expr cls* ...)
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(with-syntax ([body (generate-body #'_ #'(cls* ...))])
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#'(let ([v expr]) body))])))
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