54 lines
2.0 KiB
Scheme
54 lines
2.0 KiB
Scheme
#!r6rs
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;; Copyright (c) 2009 Derick Eddington. All rights reserved.
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;; Licensed under an MIT-style license. My license is in the file
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;; named LICENSE from the original collection this file is distributed
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;; with. If this file is redistributed with some other collection, my
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;; license must also be included.
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(library (srfi private feature-cond)
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(export
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feature-cond)
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(import
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(rnrs)
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(srfi private registry))
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(define-syntax feature-cond
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(lambda (stx)
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(define (identifier?/name=? x n)
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(and (identifier? x)
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(symbol=? n (syntax->datum x))))
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(define (make-test t)
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(define (invalid-test)
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(syntax-violation #F "invalid test syntax" stx t))
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(syntax-case t ()
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((c x ...)
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(identifier?/name=? (syntax c) (quote and))
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(cons (syntax and) (map make-test (syntax (x ...)))))
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((c x ...)
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(identifier?/name=? (syntax c) (quote or))
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(cons (syntax or) (map make-test (syntax (x ...)))))
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((c x ...)
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(identifier?/name=? (syntax c) (quote not))
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(if (= 1 (length (syntax (x ...))))
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(list (syntax not) (make-test (car (syntax (x ...)))))
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(invalid-test)))
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(datum
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(not (and (identifier? (syntax datum))
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(memq (syntax->datum (syntax datum))
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(quote (and or not else)))))
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(syntax (and (member (quote datum) available-features) #T)))
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(_ (invalid-test))))
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(syntax-case stx ()
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((_ (test . exprs) ... (e . eexprs))
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(identifier?/name=? (syntax e) (quote else))
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(with-syntax (((clause ...)
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(map cons (map make-test (syntax (test ...)))
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(syntax (exprs ...)))))
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(syntax (cond clause ... (else . eexprs)))))
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((kw (test . exprs) ...)
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(syntax (kw (test . exprs) ... (else (no-clause-true))))))))
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(define (no-clause-true)
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(assertion-violation (quote feature-cond) "no clause true"))
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)
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