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32 lines
1.2 KiB
Scheme
32 lines
1.2 KiB
Scheme
(define-syntax out
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(er-macro-transformer
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(lambda (expr rename compare)
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(for-each set-cdr! (car (cddr expr)) (cadr (cddr expr)))
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(car (cdr expr)))))
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(%define-syntax syntax-parameterize
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(lambda (expr use-env mac-env)
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(let* ((_let (make-syntactic-closure mac-env '() 'let))
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(_set! (make-syntactic-closure mac-env '() 'set!))
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(_out (make-syntactic-closure mac-env '() 'out))
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(_tmp (make-syntactic-closure mac-env '() 'tmp))
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(bindings (cadr expr))
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(body (cddr expr))
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(keywords (map car bindings))
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(transformers (map cadr bindings))
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(cells
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(map (lambda (keyword)
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(env-cell use-env keyword))
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keywords))
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(old (map cdr cells))
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(new (map (lambda (transformer)
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(make-macro
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(make-transformer
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(eval
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(make-syntactic-closure use-env '() transformer)))
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use-env))
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transformers)))
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(for-each set-cdr! cells new)
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`(,_let ((,_tmp #f))
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(,_set! ,_tmp (,_let () ,@body))
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(,_out ,_tmp ,cells ,old)))))
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