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Re: [Chicken-users] Working on format-compiler egg, question about macro
Re: [Chicken-users] Working on format-compiler egg, question about macros, eggs as wiki pages
Tue, 15 Jun 2010 15:29:30 +0200 (CEST)
From: Alejandro Forero Cuervo <address@hidden>
Subject: [Chicken-users] Working on format-compiler egg, question about macros,
eggs as wiki pages
Date: Sun, 13 Jun 2010 22:36:25 +0200
> As part of my migration from Chicken 3 to Chicken 4 I'm rewritting the
> format-modular egg into what I'm calling 'format-compiler'. I'm
> reverting many changes from it and I'm cleaning up some of the
> interfaces, to hopefully make it easier to extend (ie. to define
> control characters that do interesting things). I'm also fixing some
> bugs I've found and removing a lot of unnecessary complexity that has
> been gradually added to it with little purpose. I have a draft of
> this code here:
Very good! A solid implementation of CL-style formatting is dearly
needed, since the `format' egg is buggy and the basic `[sf]printf'
stuff is not particularly powerful. There is Shinn's formidable `fmt',
which I like to get used to (but haven't used it intensively enough).
In the end I always use `print' and `display' and normally that's
The complexity of the current `format-modular' code isn't so much the
problem - the large number of dependencies is. It would be good to
remove i18n support and for example provide hooks or another sort of
interface to extend it in a clean manner without increasing the size
and the number of base-dependencies of a bread-and-butter extension
like formatted text output.
> I'm doing a pretty large change to it: I'm separating the process of
> parsing the format string rom the process of actually generating the
> output. My thinking is that most of the time format strings are
> specified statically and never change during the execution of a
> program, as in:
> (format (current-error-port) "Evaluating ~A form: ~A~%" adj name)
> Instead of parsing the string every time, I want to parse it once and
> then use the result of that parsing on the arguments passed.
Cool - this reminds me of Common Lisp's `formatter' macro. By
seperating the format-compiler into a module, it would be possible
to use it at compile time and provide a similar facility by using
> Interestingly, this is actually allowing me to simplify the
> implementation significantly (or maybe I'm a slightly better
> programmer now than I was when I wrote format-modular?).
Well, I don't know about now, but I always envied the clean
coding style you use. :-)
> The catch is, of course, that one may memoize fmt-compiler —perhaps
> using “eq?” on the format string (for which I'll probably extend the
> memoize egg)— which means that a given statically specified format
> string would be parsed at most once and the results of that parsing
> reused through-out.
> In order to make this happen, I figured I would ask: is there a way
> for, in a macro, check if a given symbol is actually a hard-coded (ie.
> static) string? In other words, if my macro is called “format”, I
> would like “(format x "static" ...)” and “(format x foo ...)” to have
> different expansions, where the expansion for the former caches the
> results of the parsing forever and the expansion of the later only
> caches them for some time, with some heuristics. Is this possible at
(define-syntax (a-string? x r c) (string? (cadr x)))
(a-string? "abc") ~~ expands to ~~> #t
To allow using `format' like a nomrmal function (if in non-operator
position), I recommend using compiler-syntax
(`define-compiler-syntax') for `format' and the mentioned separate
module that allows using the format-compiler at
compile-time. Exporting compiler-syntax cleanly from a module is a bit
tricky, though - I will try to figure this out.
> I will add this code as an egg for both Chicken 3 and Chicken 4 once
> it's ready. I still have to add support for a few control characters.
> This is also interesting for me in that it is an experiment of storing
> an egg entirely in a wiki page. For example, the page has the
> following tag:
> author="Alejandro Forero Cuervo"
> synopsis="Creates format procedures to generate output based on format
> license="Public Domain"
> uses="posix embedded-test"
> exports="*formatter-params* ..."/>
> This is enough for Svnwiki to generate the setup, meta and Scheme
> source code files (with the blocks embedded in the wiki page) for me
> to just copy into the eggs repository. In that sense, the wiki page
> itself becomes the authoritative location for the egg. See, for
So this is effectively like a literate programming tool? An