Matt,
In fact, there might be a bug in the \1 substitution mechanism, so it is not a
bad idea to use the irregex-style replacement anyway, even if you are sticking
with POSIX REs. I noticed this a few days ago when attempting to escape
characters using a backslash. On the other hand, I could just be doing it
wrong.
This is correct:
#;354> (print (irregex-replace/all "([:@{}>])" "{foo:}" "\\" 1))
\{foo\:\}
This is obviously not correct:
#;355> (print (string-substitute "([:@{}>])" "\\\\1" "{foo:}" #t))
\\1foo\\1\\1
But, when prefixing the character with something other than backslash, \1 works
fine:
#;356> (print (string-substitute "([:@{}>])" "^\\1" "{foo:}" #t))
^{foo^:^}
This is with 4.8.0.6 (although I don’t think it matters) and the latest regex.
Jim
> On Sep 7, 2015, at 21:07, Matt Welland <[email protected]> wrote:
>
> Ok, I sort of panicked when I saw what looked like regex being deprecated
> (read my original message below if you wish). After re-reading the irregex
> egg wiki page a few times it looks like all is well assuming these two things:
>
> 1. irregex unit will continue to support reading the pcre syntax
> 2. those using the backslash substitution destination string syntax be
> prepared to write a parser/converter.
>
> As a request to the developers - please consider adding the function from the
> regex egg that parses the \N type dest strings to irregex.
>
> Thanks.
>
> Matt
> -=-
> ====== my original "panicked"message =====
>
> From a comment to Chicken-janitors regarding bug #1189 I saw this:
>
> "This seems to be an undocumented feature of the substring-replace
> function, which allows you to escape the backslash. I would recommend
> using irregex, the regex egg's API is kind of deprecated anyway, and it's
> also not very efficient."
>
> Then in the regex egg wiki page I see:
>
> "It is a thin wrapper around the functionality provided by irregex
> <http://wiki.call-cc.org/man/4/Unit%20irregex> and is mostly intended to keep
> old code working."
>
> These statements leave me a little concerned as I use the regex egg a fair
> amount and I don't have the energy to learn yet another abstraction or to go
> back and rewrite old code. More importantly I expose the use of regexes to
> users of Megatest and logpro and they have no tolerance for doing something
> considered a "standard" in a different way, especially if it means using
> something that looks like Scheme.
>
> From re-reading the irregex egg wiki page I think the only thing I rely on
> that is missing is the \1 substitution mechanism. Is there an alternative
> syntax? All I see is the following:
> (irregex-replace "(.)(.)" "ab" 2 1 "*")
> Which would be implemented using a destination of "\2\1*" in
> string-substitute. Converting an old-style destination string to the list of
> numbers and strings would not be too hard I suppose.
>
> Thanks,
>
> Matt
> -=-
>
>
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