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RE: Storing regular expressions somewhere....

From: Jay Bingham
Subject: RE: Storing regular expressions somewhere....
Date: Wed, 23 Aug 2006 18:29:06 GMT

On Wednesday, 23 August 2006 Birju Prajapati wrote:

> After digging around a bit, I found M-x regexp-builder. However, 
> doesn't seem to understand predefined character classes such as \s-
> and seems to have a different regexp syntax. Is this a bug or am I
> doing something wrong?

First, I assume that when you say regexp-builder your are actually 
referring to re-builder.el.
Although I am not an re-builder guru, I have used it quite a bit and 
I found it hard to believe that it did not understand the predefined 
character classes, so I tried it.  It works for me so you must be 
doing something wrong. ;-)

Before we get to what you could be doing wrong lets talk about what 
you mean when you say that it has a different regexp syntax.  Do you 
mean that in the default input syntax, escape characters 
(backslashes) must be doubled and double quotes must be escaped, 
which means that regular expressions generated with this syntax 
cannot be used in the interactive commands: isearch-forward-regexp, 
query-replace-regexp and replace-regexp?

Carefully reading of the commentary in re-builder reveals that there 
are four forms of input syntax provided by re-builder:
 'read', 'string', 'sregex' and 'lisp-re'
The default input syntax form is: 'read'
The syntax used by the 'read' form is the syntax that is used in the 
arguments of functions like re-search-forward and re-search-backward, 
which are used when an e-lisp function that does searching is 
written.  This syntax requires that escape characters and double 
quotes be escaped.
The syntax used by the 'string' form is the syntax that is used by 
the interactive functions isearch-forward-regexp, query-replace-
regexp and replace-regexp.
As stated in the commentary, "With the `string' syntax there's no 
need to escape the backslashes and double quotes simplifying the 
editing somewhat."  
Regarding the other two input forms the commentary states: "The other 
two allow editing of symbolic regular expressions supported by the 
packages of the same name.  (`lisp-re' is a package by me and its 
support may go away as it is nearly the same as the `sregex' package 
in Emacs)."  (I am not familiar with either of these packages and I 
don't believe that they pertain to your situation so that is all that 
will be said about them).

Now that we have that out of the way, I suspect that what you were 
doing wrong was trying to use 'string' syntax in 'read' syntax mode.

Here is a regexp that I created while reading the re-builder 
commentary after changing to string syntax (C-c C-i string RET):
It matches 31 strings and the space that follows them in the re-
builder.el file.
This regexp matches 268 words and the space that follows them in the 
re-builder.el file:

With the above regexp in the RE-Builder buffer when I change 
from 'string' to 'read' syntax the regexp changes to the following:
Changing back to 'string' syntax restores the regexp to its former 

Good luck and thanks for the opportunity to learn more about re-

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