Duncan Murdoch murdoch at stats.uwo.ca Sat Nov 8 15:41:34 CET 2008 wrote: > On 08/11/2008 7:20 AM, John Wiedenhoeft wrote: > > Hi there, > > > > I rejoiced when I realized that you can use Perl regex from within R. However, > > as the FAQ states "Some functions, particularly those involving regular > > expression matching, themselves use metacharacters, which may need to be > > escaped by the backslash mechanism. In those cases you may need a quadruple > > backslash to represent a single literal one. " > > > > I was wondering if that is really necessary for perl=TRUE? wouldn't it be > > possible to parse a string differently in a regex context, e.g. automatically > > insert \\ for each \ , such that you can use the perl syntax directly? For > > example, if you want to input a newline as a character, you would use \n > > anyway. At the moment one says \\n to make it clear to R that you mean \n to > > make clear that you mean newline... this is pretty annoying. How likely is it > > that you want to pass a real newline character to PCRE directly? > > No, that's not possible. At the level where the parsing takes place R
> has no idea of its eventual use, so it can't tell that some strings are > going to be interpreted as Perl, and others not. > > As Gabor mentioned, there have been various discussions of adding a new > syntax for strings that are parsed literally, without processing any > escapes, but no consensus on the right syntax to use. > ... [scan() example elided] ... > So I agree, it would be nice to have new syntax to allow this. Last > time this came up, I argued for something like \verb in LaTeX where the > delimiter could be specified differently in each use. Duncan TL > suggested triple quotes, as in Python. I think now that triple quotes > would be be better than the particular form I suggested. > > Duncan Murdoch Would a string with this alternate quoting be tagged (e.g., with a class that inherits from character) so that the deparser could display it in the style in which it was input? Functions which generate file names using the native Windows notation would like to have them displayed without the extra backslashes. However, adding a new class for this could mess up other things. Bill Dunlap TIBCO Software Inc - Spotfire Division wdunlap tibco.com ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
