Well, shoot. Other fearless Chickeneers already noticed this bug and marked it
as invalid in (http://bugs.call-cc.org/ticket/1189#comment:2
<http://bugs.call-cc.org/ticket/1189#comment:2>) due to order of operations.
Basically, in “\\\\1” the backslash is itself backslashed, so it becomes the
text \1.
Anyway, the upshot is, the irregex version is better.
Jim
> On Sep 9, 2015, at 23:24, Jim Ursetto <zbignie...@gmail.com> wrote:
>
> 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 <smb://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 <mattrwell...@gmail.com
>> <mailto:mattrwell...@gmail.com>> 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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