Re: Wow, Lisp Reader !!

Yes, I have that for myself. 

Perhaps I just need to polish it a bit harder. For the embedded colon chars in my angle input, I currently have to write #N|12:42:33.25| or #N”12:42:33.25” so that I have either a symbol or a string to take apart. But if I back up a bit and do the read-chars myself, then I ought to be able to get around this.

That #N format also gives me complex notation like 1.2+2.7j as well as dates like 2025/05/23. Those can be written directly into a Sexpr enclosed by a WITH-EXTENDED-NUMBER-SYNTAX macro that just traces the Sexpr tree and tries interpreting every symbol as one of these extended number formats.



> On May 23, 2026, at 15:00, Jon Boone <[email protected]> wrote:
> 
> Would either of these approaches possibly work?
> Like '$math_expr$' in LaTeX triggers in-line math-mode, you can create a macro-key sequence that switches to your custom Readtable just for that format and have the macro evaluate the input to generate the proper character sequence for normal Readtable usage, or
> I think you can create a custom macro-key in the default Readtable that lets you type your preferred syntax. This macro would un-read the previous symbols with the ':' delimiters and re-format them into output compatible with the normal read-table.
> 
> —jon
> 
> 
> On Sat, May 23, 2026 at 5:41 PM David McClain (as dbm at refined-audiometrics dot com) <[email protected] <mailto:[email protected]>> wrote:
>> Holy smokes… Common Lisp did such an amazing job with everything else, and especially CLOS. But now that I am old, I want to specialize the Lisp Reader for myself. I get really wearing not being able to enter DD:MM:SS for Right Ascensions and Declinations.
>> 
>> But gobsmack'ingly, the Common Lisp Reader is hugely resistant to customization. The HyperSpec hints that custom readers should be possible:
>> 
>> 2.1.4 Character Syntax Types
>> 
>> The Lisp reader <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_reader> constructs an object <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_o.htm#object> from the input text by interpreting each character <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_c.htm#character> according to its syntax type <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_s.htm#syntax_type>. The Lisp reader <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_reader> cannot accept as input everything that the Lisp printer <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_printer> produces, and the Lisp reader <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_reader> has features that are not used by the Lisp printer <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_printer>. The Lisp reader <https://www.lispworks.com/documentation/HyperSpec/Body/26_glo_l.htm#lisp_reader> can be used as a lexical analyzer for a more general user-written parser.
>> 
>> 
>> 
>> And yet, there are no functions to allow interrogation of the Readtable for character syntax types corresponding to any particular character, except for those that are marked as macro characters.
>> 
>> 
>> Other, macro characters, like tic (apostrophe) #\’ should really only carry meaning at the leading edge of a symbol name. But it serves as a stopping delimiter in the Lisp Reader so that you cannot have symbol names like Thing and Thing’, without writing them as |Thing’|.
>> 
>> Interestingly, the colon character, #\:, which is used to separate package names from symbol names, is *NOT* shown as anything special in the HyperSpec. It is simply listed as a constituent character.
>> 
>> Maddeningly, LW chose to intercept this character with eager resolution, rather than allowing it to just become absorbed as a compound symbol token for later analysis. And there are no CL Hooks to be found that allows for alternate interpretations.
>> 
>> So I find it totally mystifying that this corner of Common Lisp should be so comparatively backwards.
>> 
>> 
>> 
>> [ I apologize if I come off too harsh. I cut my teeth on Forth, which has no restrictions, at the observatories many decades ago… ]
>>