fix: README -> README.md

ta6ob/examples/macro.ss

@@ -0,0 +1,89 @@
+;;; Copyright (C) 1989 R. Kent Dybvig
+
+;;; Permission is hereby granted, free of charge, to any person obtaining a
+;;; copy of this software and associated documentation files (the "Software"),
+;;; to deal in the Software without restriction, including without limitation
+;;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
+;;; and/or sell copies of the Software, and to permit persons to whom the
+;;; Software is furnished to do so, subject to the following conditions:
+;;; 
+;;; The above copyright notice and this permission notice shall be included in
+;;; all copies or substantial portions of the Software.
+;;; 
+;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+;;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+;;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+;;; THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+;;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+;;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+;;; DEALINGS IN THE SOFTWARE. 
+
+;;; PCScheme/MacScheme "macro" defined in terms of "syntax-case":
+
+(define-syntax macro
+  (lambda (x)
+    (syntax-case x ()
+      ((_ name fcn)
+       #'(define-syntax name
+           (lambda (x)
+             (syntax-case x ()
+               ((k . stuff)
+                (datum->syntax-object #'k
+                  (fcn (syntax-object->datum x)))))))))))
+
+
+;;; PCScheme/MacScheme "macro" defined in terms of "extend-syntax":
+;;; requires (current-expand eps-expand)
+
+;(extend-syntax (macro)
+;   [(macro name fcn)
+;    (eval-when (compile load eval)
+;       (let ([f fcn])
+;          (extend-syntax (name)
+;             [anything
+;              ((with ([w 'with]) w)
+;               ([v (f 'anything)]) v)])))])
+
+;;; The strange expression "(with ([w 'with]) w)" is used to insert the
+;;; keyword "with" into the expansion.  The "eval-when" in the expansion is
+;;; necessary to allow macros defined in a file to be used later in the
+;;; file, even if the file is compiled with "compile-file".  If it were
+;;; left out, the implicit "eval-when" wrapped around the "extend-syntax"
+;;; would cause it to be evaluated, but without the enclosing "let"
+;;; expression.  The enclosing "let" expression is necessary to cause the
+;;; function to be evaluated once, which may be important if the function
+;;; something other than a simple lambda expression.
+
+
+;;; PCScheme/MacScheme "macro" defined in terms of "define-syntax-expander":
+;;; requires (current-expand eps-expand)
+
+;(extend-syntax (macro)
+;   [(macro name fcn)
+;    (define-syntax-expander name
+;       (let ([f fcn])
+;          (lambda (x e) (e (f x) e))))])
+
+;;; The "eval-when" is not necessary because "define-syntax-expander"
+;;; expands into an "eval-when" expression, and the "let" expression is
+;;; tucked inside the "define-syntax-expander" expression.
+
+;;; If you want to see the expander generated by either of the above
+;;; "extend-syntax" definitions looks like, use "extend-syntax/code" in
+;;; place of "extend-syntax":
+
+;;; > (extend-syntax/code (macro)
+;;;      [(macro name fcn)
+;;;       (define-syntax-expander name
+;;;          (let ([f fcn])
+;;;             (lambda (x e) (e (f x) e))))])
+;;;
+;;; (lambda (x e)
+;;;    (unless (procedure? e)
+;;;       (error 'macro "~s is not a procedure" e))
+;;;    (e (cond
+;;;          [(syntax-match? '(macro * *) x)
+;;;           `(define-syntax-expander ,(cadr x)
+;;;               (let ([f ,@(cddr x)]) (lambda (x e) (e (f x) e))))]
+;;;          [else (error 'macro "invalid syntax ~s" x)])
+;;;       e))