On Sun 13 Sep 2009 23:17, Neil Jerram <n...@ossau.uklinux.net> writes:
> I think that's the right eventual question, anyway. The context is > running Alan Grover's mod_lisp-for-guile in 1.9.2. > > The mod_lisp-for-guile code includes a use of read-hash-extend to > define a syntax for a compiled regular expression - so that you can > write things like > > (if (#m/^Error: +/ line) > ...) > > with a similar effect to Perl > > if (line ~= /^Error: +/) > ... > > So: > > (read-hash-extend #\m (lambda (c port) > ... > (lambda (string) > ...))) > > In other words, the custom reader procedure returns another > procedure. So what happens when you compile this file? You would have to serialize that procedure somehow, a procedure that could be a closure, etc... No, I think all macros have to return syntax and not values. This particular case is a bit unfortunate, though. You really want to compile the regex once, preferably at compile-time... ideally the regex compiles to scheme, and thence to bytecode/native code, but that's not how things are right now. So yes, I think the best we can do is to do what you did: > (define-public (make-regexp-fn regexp-string) > (lambda (string) > ...)) And make-regexp-fn should memoize results. > but I wonder if there is a case for supporting the code as it was > before, by I'm afraid not, because you need to be able to compile a file to bytecode, write it out to disk, then load it later. > Also, is it definitely correct to call read-hash-extend procedures > first, and do the psyntax pass later? I guess it must be, as we need > to call the read-hash-extend procedure in order even to determine the > extent of the relevant lexeme. Right. More thought (and documentation!) is needed here, though. Andy -- http://wingolog.org/
