Subject: Re: porting from a dialect with a different keyword style
From: Erik Naggum <>
Date: 1998/07/29
Newsgroups: comp.lang.lisp
Message-ID: <>

* Jon Dyte
| However talk has symbols which end in ':' and behave like a
| keyword -> evaluate to themeselves.

  ouch.  been there, suffered that.

| Can anyone suggest a quick method of allowing this to be read in?  CL
| thinks the lhs of the colon refers to a package....

  quick?  maybe.  dirty?  oh, yes.  :)

  first, you make #\: a terminating macro character that returns a unique
  symbol, instead of being a constituent character that causes the symbol
  reader to attempt to absorb it only to barf on you.  second, you advise
  READ to hack a returned list to convert a symbol followed by the special
  colon marker into a keyword and then skip the colon marker.  (I forget
  why we have to advise EXCL::READ1 instead of CL:READ.)

(defvar *ilog-readtable* (copy-readtable nil)
  "Readtable modified to read keywords that _end_ in colon.")

(defvar *colon* (list #\:)
  "Special colon marker to replace final colon in symbols read.")

(defun colon-reader (stream character)
  "Replace all read colons with the special colon marker.  Undone later."
  (declare (ignore stream character))

(set-macro-character #\: 'colon-reader nil *ilog-readtable*)

(defadvice excl::read1 (ilog-fixup :after)
  "Undo the damage done by COLON-READER and intern keywords properly."
  (when (and (eq *readtable* *ilog-readtable*)
	     (listp (first values)))
    (loop for tail on (first values)
	  when (and (symbolp (first tail)) (eq *colon* (second tail)))
	  do (setf (first tail) (intern (symbol-name (first tail))
		   (second tail) nil
		   (cdr tail) (cddr tail))
          when (eq *colon* (first tail))
          do (error "Colon reader needs more work."))))

  you can now do stuff like

(let ((*readtable* *ilog-readtable*))
  (read-from-string "(define-cpp-function whatever super: t fumble: yes)"))
=> (define-cpp-function whatever :super t :fumble yes)

  voilà, as the Ilog Talk people would probably say.

  CAVEAT: this was sufficient for reading DSSSL, and may not be sufficient
  for anything else.  use at your own risk.

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