Re: Wow, Lisp Reader !!

My 0.02 EUR opinion is that reader macros do get you quite a lot.
Incidentally the #I for infix (math) has been around for ages; check the
CMU repository.

What I noticed is that Julia takes one step more.  you write #symbol... so
you have "reader dispatching "symbols".  Which opens up many doors (some
with monsters behind, but ...)

Cheers

Marco


On Sun, May 24, 2026 at 10:58 AM Tim Bradshaw (as tfb at cley dot com) <
[email protected]> wrote:

> On 23 May 2026, at 23:18, David McClain (as dbm at refined-audiometrics
> dot com) <[email protected]> wrote:
>
>
> 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.
>
>
> The problem with this is that you need to know when to stop.  Presumably
> '#N12:42:123(' is legal (leaving an open paren to be read, so the next form
> to be read being a list) but '#N12:42:123x' should not be.
>
> You really need access to the syntax types of characters and you don't
> have that.
>
> I'm guessing that the reason it's all so opaque is that the reader only
> has to behave *as if* the things the spec describes are true: it might
> internally be doing something quite different, especially for interactive
> use.  Exposing more of it would tend to force it to *actually* behave the
> way it's meant to, which would constrain implementations a lot more.
>
> But it's annoying.  What I do is the delimiter thing: write something that
> will read characters up to an unescaped delimiter and hand them to whatever
> it is.  So my syntax would be '#N[...]', or '#N/.../' read-delimited-list
> is not how you need to do this because the characters you read need to be
> uninterpreted.
>
> --tim
>


-- 
Marco Antoniotti, Professor, Director         tel. +39 - 02 64 48 79 01
DISCo, University of Milan-Bicocca U14 2043   http://dcb.disco.unimib.it
Viale Sarca 336
I-20126 Milan (MI) ITALY

REGAINS: https://regains.disco.unimib.it/