Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!agate!eos!ptolemy!raymond
From: raymond@ptolemy.arc.nasa.gov (Eric A. Raymond)
Newsgroups: comp.lang.lisp
Subject: Re: readmacros in CL: getting "[", "]" to work as "(", ")"
Message-ID: <1053@ptolemy.arc.nasa.gov>
Date: 15 Mar 89 02:33:33 GMT
References: <424@soi.UUCP> <2848@kalliope.rice.edu>
Reply-To: raymond@ptolemy.arc.nasa.gov (Eric A. Raymond)
Organization: NASA Ames Research Center, Moffett Field, CA
Lines: 45

In article <2848@kalliope.rice.edu> dorai@titan.rice.edu (Dorai Sitaram) writes:
>Could someone please tell me how to define brackets ("[", "]") as
>macro characters in CommonLisp so that they have the same effect as
>the usual parens (but make for more readable code)? 


Here goes, but I bet you'll never use them if you let your editor do
your formatting (and are too lazy to rewrite the indenter).  

;;; This may reference LISPM specific code

(defun bracket->list-reader (stream sub-char)
  "This allows you to use the characters [ and ] to delimit lists.
  This is especially useful when using nested list structures.  (i.e.
  (let ([this 1] [that 2]) (+ this that)) ) One drawback is that the
  editor will not flash the opening/closing bracket like it will a
  parenthesis.  Also, it will not catch unbalanced brackets or indent
  some special forms properly.  Hint: Use brackets for inner most
  forms (i.e. (let ([a 1]) ) not (let [(a 1)])) Do NOT mix parenthesis
  and brackets."
  (declare (ignore sub-char))
  (values (read-delimited-list #\] stream t)))
(set-macro-character #\[ #'bracket->list-reader T)
(set-macro-character #\] (get-macro-character #\)))


Here's something for progn's:


(defun curly-brace->progn-reader (stream sub-char)

  "This allows a shorthand for progn (ala C). Uses balance pairs of {}
   to delimit progns."
  
  (declare (ignore sub-char))
  (list* 'progn (read-delimited-list #\} stream t)))
(set-macro-character #\{ #'curly-brace->progn-reader T)
;;; This prevents } from being part of form
(set-macro-character #\} (get-macro-character #\)))



-- 
Eric A. Raymond  (raymond@pluto.arc.nasa.gov)
Nothing left to do but :-) :-) :-)