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Newsgroups: comp.lang.scheme.scsh
Subject: Arc a la carte
From: walter@pelissero.org (Walter C. Pelissero)
Message-ID: <86r8o67525.fsf@hyde.lpds.sublink.org>
Date: 31 Jan 2002 18:23:30 +0000


After reading http://www.paulgraham.com/arc.html I wasn't left very
impressed especially because most of that can be achieved with macros
in Common Lisp.

Nevertheless there was a feature I found cool.  The square bracket
sexp that expands to a single argument lambda expression.  So that I
can do things like:

  (map [/ _ 2] '(2 4 6 8 10))
  (cond ((regexp-exec r) => [match:substring _ 1]) ...)

instead of

  (map (lambda (x) (/ x 2)) '(2 4 6 8 10))
  (cond ((regexp-exec r) => (lambda (m) (match:substring m 1))) ...)

After a few minutes of searching I found out that Scheme48 has
surprising similarities with CL when it comes to syntax macros.
So here is the trick:

--- /usr/home/wcp/Projects/others-cvs/scsh/scsh/scsh/scsh-read.scm	Fri Aug  6 14:28:02 1999
+++ scsh/scsh-read.scm	Thu Jan 31 17:40:09 2002
@@ -29,6 +29,15 @@
 
 (define-sharp-macro #\! script-skip)
 
+;;; Arc  la carte
+(set-standard-read-macro! #\[ #t
+  (lambda (c port)
+    (list 'lambda '(_) (sub-read-list c port))))
+(set-standard-read-macro! #\] #t
+  (lambda (c port)
+    c port
+    close-paren))
+
 
 ;;; Readme and readme are distinct symbols.
 

I'm not suggesting Scsh or Scheme48 to pick up this syntactic sugar
nor I wish Scheme would fall, together with Perl, in the hell of
syntactic crypticism.  This has been written just as a funny exercise
in Scsh hacking and... Arc mocking, of course.  On the other hand I
wish this sort of things were be possible without patching Scsh (or
Scheme48).

-- 
walter pelissero
http://www.pelissero.de

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