Re: Wow, Lisp Reader !!

It’s white spaces and any terminating macro (or dispatching) macro
character. And this can be queried with gat-macro-character

So for example (foo’bar) has two elements but (foo#bar) has only one while
(foo #p "bar") has two.
There is a list of white space in the standard-character set (you can
extend it with Unicode), and query the read table for the other terminating
macro characters. See
(map nil 'print
(com.informatimago.tools.reader-macro:list-all-macro-characters))
In
https://github.com/informatimago/lisp/blob/master/tools/reader-macro.lisp

-- 
__Pascal Bourguignon__
+33623171770
[email protected]


Le dim. 24 mai 2026 à 16:33, David McClain <[email protected]> a
écrit :

> Point of curiosity…
>
> I see that the Lisp community has chosen to allow not only whitespace, but
> also parentheses, as parse stopping point. Totally reasonable, given the
> basis of the language in Sexprs. But why also Quote, Backquote? Also
> Semicolon - seems reasonable. Comma and Vertical Bar?
>
> I can easily envision wanting symbol names ending in a quote, as in X’
> (for x-prime).
>
>
> On May 24, 2026, at 07:14, David McClain (as dbm at refined-audiometrics
> dot com) <[email protected]> wrote:
>
>
>
> On May 24, 2026, at 02:29, Pascal Bourguignon <[email protected]>
> wrote:
>
> (defun install-angle-reader (&optional (readtable *readtable*))
>   "Install the angle reader macro on digits and signs."
>   (dolist (c '(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9 #\+ #\-)) ; <- the
> magic is here ;-)
>     (set-macro-character c #'read-angle-or-fallback t readtable))
>   readtable)
>
>
>
> Now this is interesting, but it also illustrates the control point I just
> described. As long as you are inside a Reader Macro, you have absolute
> control. Pascal has exerted the control on individual digit chars. That
> seems a brilliant way to approach things!
>
> Your point about prefix mapping the parser might be theoretically valid,
> i.e., first two chars determines the route. But in practice, LW Reader also
> uses the special chars for stopping parses. That is to say that a Quote
> will stop an ongoing number parse, unless you preemptively take control
> through a reader macro doing READ-CHAR. Depending on the Reader at the READ
> level will fail your intentions.
>
>
>