Okay what. I've long relied on the behavior of regexp-replace* to single
out a number of substrings within a big string, and let me mangle those
substrings in a programmatic fashion. Example:
(regexp-replace*
#rx"([a-z]+) ([a-z]+)" "red fox, blue seal. red trout, blue trout!"
(lambda (total color what)
(cond
((equal? color "red") (string-append what " in socks"))
((equal? what "trout") (string-append color " fish"))
(else (string-append color " " what)))))
=> "fox in socks, blue seal. trout in socks, blue fish!"
Recently every program of mine that did that, they all started erroring
out on contract errors. I took a look at the code and was shocked to
find this in racket/private/string.rkt:
(check
replacement
(sub buf mstart mend))
which effectively becomes (replacement (sub buf mstart mend)).
It gives no access to subexpressions, and only matches on the entire
pattern. For patterns like #rx"(someheader*)([0-9a-zA-Z]+)(somefooter*)"
that's especially nasty, since I need those three fields separate, but
there might not be a particular character sequence uniquely separating them.
Is there no way to replace all instances of an expression in a string
with some combination of its sub-expressions? I really can't use the
"\\1 \\2" stuff since I'm replacing stuff that could either be a hex
number, a decimal number, or a standard abbreviated name. Was this
support removed for a reason, or was it just too much of a hassle to
figure out? Is there some other procedure that does this now?
_________________________________________________
For list-related administrative tasks:
http://lists.racket-lang.org/listinfo/users
