[racket] Some design "whys" of regexps in Racket

At Sat, 4 Jun 2011 00:09:40 -0300, Rodolfo Carvalho wrote:
> Eli says that
> 
> (BTW, Racket's solution is something that is done in many other
> > languages too.)
> 
> 
> 
> I come from Python where I can write
> 
> >>> re.findall("\d{2}", "06/03/2011")
> ['06', '03', '20', '11']
> 
> And printing the string that I used for my regexp gives:
> 
> >>> print "\d{2}"
> \d{2}

Isn't that only because "\d" isn't an escape in strings? While Racket
complains about a "\" that doesn't form an escape sequence, Python
treats the "\" as a literal (while Ruby effectively ignores the "\").

Compare to the Python example

 >>> re.findall("a\b", "a ")
 []
 >>> re.findall("a\\b", "a ")
 ['a']

Since "\b" is an escape that means ASCII 8, to get a backslash followed
by a "b" in a regexp (to indicate a word boundary), you need to use
"\\b".