comp.lang.lisp Google Group

Re: How to tell reader that strings are delimited with `<' and `>' ?

p...@informatimago.com (Pascal J. Bourguignon) — Sun, 11 Nov 2009 22:15:54 UT

Ah well, you're right, CLHS set-syntax-from-char says:
A macro definition from a character such as " can be copied to
another character; the standard definition for " looks for another
character that is the same as the character that invoked it. The
definition of ( can not be meaningfully copied to {, on the other

Re: How to tell reader that strings are delimited with `<' and `>' ?

vniko...@pobox.com (Vassil Nikolov) — Sun, 11 Nov 2009 22:09:32 UT

^^^^
I made no claims about CLHS; but even ignoring that, CLHS still does
not say that #\"'s macro character function expects _only_ a #\" as
the string terminator.
In other words, after (SET-SYNTAX-FROM-CHAR #\< #\"), the theory
that explains (READ-FROM-STRING "<foo>")'s error with the absence of

Re: How to tell reader that strings are delimited with `<' and `>' ?

p...@informatimago.com (Pascal J. Bourguignon) — Sun, 11 Nov 2009 22:03:10 UT

Why not read <label name> as LABEL-NAME then?

Re: How to tell reader that strings are delimited with `<' and `>' ?

mirko.vuko...@gmail.com (Mirko) — Sun, 11 Nov 2009 21:53:14 UT

(defun set-bar (label-name)
(gnuplot-set-command "bar" label-name)) ;;pseudocode
Previous post was sent before being finished. Fixed above.

Re: How to tell reader that strings are delimited with `<' and `>' ?

mirko.vuko...@gmail.com (Mirko) — Sun, 11 Nov 2009 21:51:32 UT

The reason I have to read as string is as follows:
<foo> denotes entry of an explicit value. In my interface, I would
have
(defun set-bar (foo)
(gnuplot-set-command "bar" foo) ;; pseudocode
However, in some cases, GNUPLOT has a compound name: <label name>,
which I will have to translate into
(defun set-bar (label-name)

Re: How to tell reader that strings are delimited with `<' and `>' ?

p...@informatimago.com (Pascal J. Bourguignon) — Sun, 11 Nov 2009 21:36:05 UT

CLHS 2.4.5 says:
The double-quote is used to begin and end a string. When a
double-quote is encountered, characters are read from the input
stream and accumulated until another double-quote is
encountered. If a single escape character is seen, the single
escape character is discarded, the next character is accumulated,

Re: How to tell reader that strings are delimited with `<' and `>' ?

vniko...@pobox.com (Vassil Nikolov) — Sun, 11 Nov 2009 21:34:18 UT

P.S. Depending on what _exactly_ you are processing [*], you might
get away with the kludge of
(set-syntax-from-char #\< #\Space)
(set-syntax-from-char #\> #\Space)
to read the above as the symbol LABEL (I see no reason why one would
insist on reading strings here).
_________
[*] e.g. whether such tags may contain non-constituent characters

Re: How to tell reader that strings are delimited with `<' and `>' ?

vniko...@pobox.com (Vassil Nikolov) — Sun, 11 Nov 2009 21:24:08 UT

CL-USER> (set-syntax-from-char #\< #\")
CL-USER> (set-syntax-from-char #\> #\")
It actually expects the same delimiter at the end as in the
beginning (maybe not according to CLHS, but to CLtL), so after the
above, <foo< would be read as "foo" and so would >foo> (which is
still not what is desired, of course).

Re: How to tell reader that strings are delimited with `<' and `>' ?

p...@informatimago.com (Pascal J. Bourguignon) — Sun, 11 Nov 2009 21:07:49 UT

To be able to use <abc> in lisp sources, just run:
(set-macro-character #\< (function bracket-string-reader) *readtable*)
on the REPL readtable. Above I showed a benign example installing the
reader macro on a temporary local readtable, but of course you can
modify directly *readtable*.
This errors comes from the fact that the predefined reader macro for

Re: How to tell reader that strings are delimited with `<' and `>' ?

vniko...@pobox.com (Vassil Nikolov) — Sun, 11 Nov 2009 20:43:57 UT

The latter is exactly achieved by doing the former (i.e. by suitably
defining #\< as a macro character), so in what way would you like to
do better?
Note that the only way the (standard Common Lisp) reader algorithm
can return a string is through the use of macro characters (only
numbers and symbols are produced from extended tokens).

Re: How to tell reader that strings are delimited with `<' and `>' ?

mirko.vuko...@gmail.com (Mirko) — Sun, 11 Nov 2009 20:43:17 UT

On Nov 8, 3:01 pm, p...@informatimago.com (Pascal J. Bourguignon)
wrote:
Thanks Pascal, that is what I had so far.
I was looking for something like this (and which does not work):
CL-USER> (set-syntax-from-char #\< #\")
T
CL-USER> (set-syntax-from-char #\> #\")
T
CL-USER> (read-from-string "<abc>")

Re: Is there a better way to store this?

p...@p-cos.net (Pascal Costanza) — Sun, 11 Nov 2009 20:37:17 UT

Are you aware of the following link?
[link]
Pascal

Re: Ron Garret considered harmful

vniko...@pobox.com (Vassil Nikolov) — Sun, 11 Nov 2009 20:23:50 UT

Thank you so much for your guidance, even though I was actually
objecting to the statement that "only a monkey" would have used
"shrunk" as the past tense form (instead of "shrank"), which is
somewhat different.
Which is the body that issues pronouncements when a hitherto
incorrect form becomes correct in the English language, or a

Re: How to tell reader that strings are delimited with `<' and `>' ?

p...@informatimago.com (Pascal J. Bourguignon) — Sun, 11 Nov 2009 20:01:52 UT

(defun bracket-string-reader (stream ch)
(declare (ignore ch))
(coerce (loop for ch = (read-char stream)
until (char= #\> ch)
collect ch) 'string))
(let ((*readtable* (copy-readtable nil)))
(set-macro-character #\< (function bracket-string-reader) *readtable*)

How to tell reader that strings are delimited with `<' and `>' ?

mirko.vuko...@gmail.com (Mirko) — Sun, 11 Nov 2009 19:55:31 UT

Hello,
I am parsing a file that has snippets such as
<label>
I would like to coax the reader to return a string "label". Right
now, I have defined a macro character #\< to collect characters from
the input stream until the matching > is found. But I wonder if I can
coax the reader to interpret <label> as a "label" string.