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90 lines
3.6 KiB
Scheme
90 lines
3.6 KiB
Scheme
;;; Copyright (C) 1989 R. Kent Dybvig
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;;; Permission is hereby granted, free of charge, to any person obtaining a
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;;; copy of this software and associated documentation files (the "Software"),
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;;; to deal in the Software without restriction, including without limitation
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;;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
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;;; and/or sell copies of the Software, and to permit persons to whom the
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;;; Software is furnished to do so, subject to the following conditions:
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;;;
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;;; The above copyright notice and this permission notice shall be included in
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;;; all copies or substantial portions of the Software.
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;;;
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;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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;;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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;;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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;;; THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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;;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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;;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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;;; DEALINGS IN THE SOFTWARE.
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;;; PCScheme/MacScheme "macro" defined in terms of "syntax-case":
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(define-syntax macro
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(lambda (x)
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(syntax-case x ()
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((_ name fcn)
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#'(define-syntax name
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(lambda (x)
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(syntax-case x ()
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((k . stuff)
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(datum->syntax-object #'k
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(fcn (syntax-object->datum x)))))))))))
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;;; PCScheme/MacScheme "macro" defined in terms of "extend-syntax":
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;;; requires (current-expand eps-expand)
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;(extend-syntax (macro)
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; [(macro name fcn)
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; (eval-when (compile load eval)
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; (let ([f fcn])
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; (extend-syntax (name)
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; [anything
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; ((with ([w 'with]) w)
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; ([v (f 'anything)]) v)])))])
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;;; The strange expression "(with ([w 'with]) w)" is used to insert the
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;;; keyword "with" into the expansion. The "eval-when" in the expansion is
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;;; necessary to allow macros defined in a file to be used later in the
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;;; file, even if the file is compiled with "compile-file". If it were
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;;; left out, the implicit "eval-when" wrapped around the "extend-syntax"
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;;; would cause it to be evaluated, but without the enclosing "let"
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;;; expression. The enclosing "let" expression is necessary to cause the
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;;; function to be evaluated once, which may be important if the function
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;;; something other than a simple lambda expression.
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;;; PCScheme/MacScheme "macro" defined in terms of "define-syntax-expander":
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;;; requires (current-expand eps-expand)
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;(extend-syntax (macro)
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; [(macro name fcn)
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; (define-syntax-expander name
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; (let ([f fcn])
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; (lambda (x e) (e (f x) e))))])
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;;; The "eval-when" is not necessary because "define-syntax-expander"
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;;; expands into an "eval-when" expression, and the "let" expression is
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;;; tucked inside the "define-syntax-expander" expression.
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;;; If you want to see the expander generated by either of the above
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;;; "extend-syntax" definitions looks like, use "extend-syntax/code" in
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;;; place of "extend-syntax":
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;;; > (extend-syntax/code (macro)
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;;; [(macro name fcn)
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;;; (define-syntax-expander name
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;;; (let ([f fcn])
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;;; (lambda (x e) (e (f x) e))))])
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;;;
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;;; (lambda (x e)
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;;; (unless (procedure? e)
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;;; (error 'macro "~s is not a procedure" e))
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;;; (e (cond
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;;; [(syntax-match? '(macro * *) x)
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;;; `(define-syntax-expander ,(cadr x)
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;;; (let ([f ,@(cddr x)]) (lambda (x e) (e (f x) e))))]
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;;; [else (error 'macro "invalid syntax ~s" x)])
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;;; e))
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