writing out expressions prepended by #. - comp.lang.lisp

Message from discussion writing out expressions prepended by #.

Erik Naggum

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More options Apr 27 2001, 10:34 pm

Newsgroups: comp.lang.lisp

From: Erik Naggum <e...@naggum.net>

Date: Sat, 28 Apr 2001 02:34:52 GMT

Local: Fri, Apr 27 2001 10:34 pm

Subject: Re: writing out expressions prepended by #.

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* Kent M Pitman

> The only disadvantage of #.(...) is that a lot of people bind *read-eval*
> when reading forms, and in that case you'll lose on the re-read. To
> counteract that, you might be better off to take some other dispatch on #
> and make something similar to #S but with user-definable characteristics.
:
> I seem to recall I tried to get the committee to generalize its effect
> but for some reason it didn't go through--maybe it was after the feature
> freeze...

I have taken to define #/ as a reader-macro akin to the format control,
to read _registered_ types with associated functions, as I ran out of
convenient ways to specify classes and such.

In this particular case, #/point/(1 2 3), would require a registered type
named point with an associated reader function that that would read as
many arguments as it needs using whatever printer controls and reader
functions it pleased, but it would of course be the question of more or
less reasoanble usages, as with every other powerful mechanism. E.g.,
#/ip/192.168.150.155/26 could mean the address and a 26-bit mask for
routing or matching purposes, whild #/ip/192.168.150.155:5555 could mean
an address and a port number. And #/md5/0123456789abcdeffedcba9876543210
could mean the hexadecimal representation of an MD5 sum.

Given this framework, would be a very simple task to supply macros that
defined and registered reader functions and corresponding print-object
methods for new classes.

#:Erik
--
I found no peace in solitude.
I found no chaos in catastrophe.
-- :wumpscut:

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