Re: [R] Parsing regular expressions differently - feature request

From: Wacek Kusnierczyk <Waclaw.Marcin.Kusnierczyk_at_idi.ntnu.no>
Date: Sun, 09 Nov 2008 00:37:49 +0100

Wacek Kusnierczyk wrote:

> Duncan Murdoch wrote:
>   
>>>>> Here's a quick hack to achieve the impossible:
>>>>>           
>>>> That might solve John's problem, but I doubt it.  As far as I can see
>>>> it won't handle \L, for example.
>>>>
>>>>         

>>> well, it was not supposed to. it addresses the need for doubling
>>> backslashes when a backslash character is an element of the regex.
>>>
>> \L could be an element of a regex in Perl.
>>
>>     

you should perhaps specify what you mean by 'could be an element of a regular expression'. there is a difference between a regular expression and a string specifying it.

in /\LA/, i'd say the string between the slashes contains three characters, but the regex contains just one; there is no \L in the regex, and no backslash either.

in /\\LA/, i'd say the string contains four characters, but the regex just three; there is a backslash there, but no \L.

just try qr/\L/ (that's an empty pattern), qr/\LA/ (that's a one-character pattern equivalent to qr/a/), and qr/\\LA/.

in a sense, \L is just a macro used in constructing regexes, but it has no place in a regex. in this view, "\LA" and "a" are two dstinct strings specifying the same regex (try qr/\LA/ eq qr/a/).

vQ



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