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From: tim@hpfcbig.SDE.HP.COM (Tim Mikkelsen)
Newsgroups: comp.lang.lisp.x
Subject: Re: Accessing READTABLE in Xlisp 2.1
Message-ID: <1170011@hpfcbig.SDE.HP.COM>
Date: 21 Sep 90 02:57:54 GMT
References: <1990Sep20.003513.14808@cs.utk.edu>
Organization: HP SESD, Fort Collins, CO
Lines: 68

set-macro-character
________________________________________________________________________

type: defined function (closure) 
location: extension
source file: init.lsp
Common LISP compatible: related
supported on: all machines

SYNTAX

(set-macro-character <char-num> <function>  [ <termflag> ] )
	<char-num>	-	an integer expression
	<function>	-	a function definition
	<termflag>	-	an expression - NIL or non-NIL

DESCRIPTION

The SET-MACRO-CHARACTER function installs the code that will be executed
when the specified  character  <char-num>  is  encountered  by the XLISP
reader.  The  <function> is placed in the  *READTABLE*  system  variable
which  contains  the  reader  table  array.  The  table  is 128  entries
(0..127)  for each of the 7-bit  ASCII  characters  that XLISP can read.
Each  entry in the  table  must be one of NIL,  :CONSTITUENT,  :SESCAPE,
:MESCAPE,  :WHITE-SPACE, a :TMACRO dotted pair or a :NMACRO dotted pair.
The SET-MACRO-CHARACTER function only allows you to put in a terminating
read-macro  function (:TMACRO) or a non-terminating  read-macro-function
(:NMACRO).  If  the   <termflag>  is  present  and  non-NIL,   then  the
<function> will be put in *READTABLE* as a :TMACRO entry.  If <termflag>
is not present or NIL, then  <function>  will be put in *READTABLE* as a
:NMACRO entry.  The <function> can be a built-in  read-macro function or
a user  defined  defun  symbol or a lambda  expression.  The  <function>
takes two parameters, an input stream specification, and an integer that
is  the  character  value.  The  <function>  should  return  NIL  if the
character  is  'white-space'  or a value  CONSed  with NIL to return the
value.  The function SET-MACRO-CHARACTER always returns T.

EXAMPLES

	(print "hi") % comment			; prints  "hi"  and gives
						; error: unbound variable - %
						; because percent is viewed 
						; as a variable
						;
	(setq semi (get-macro-character #\;))	; get semi-colon code
						;	
	(SET-MACRO-CHARACTER #\% semi T)	; set % to work as a comment
						;
	(print "hi") % comment			; prints  "hi" and no error
						; because % is now a comment
						; character in *READTABLE*

NOTE:
In the normal XLISP system the following characters have code associated
with them in the *READTABLE*:

		" # ' ( ) , ; `

NOTE:
The functions GET-MACRO-CHARACTER and SET-MACRO-CHARACTER are created in
the INIT.LSP file.  If they do not exist in your XLISP system, you might
be having a problem with  INIT.LSP.  Before you start XLISP, look in the
directory  you  are  currently  in,  and  check  to see if  there  is an
INIT.LSP.

COMMON LISP COMPATABILITY:
The SET-MACRO-CHARACTER  function is somewhat related to the Common LISP
SET-DISPATCH-MACRO-CHARACTER function.