emacs regex has a odd pecularity in that it needs a lot backslashes.
More specifically, a string first needs to be properly escaped, then
this passed to the regex engine.

For example, suppose you have this text “Sin[x] + Sin[y]” and you need
to capture the x or y.

In emacs i need to use
“\\(\\[[a-z]\\]\\)”
for the actual regex
“\(\[[a-z]\]\)”.

Here's somewhat typical but long regex for matching a html image tag

(search-forward-regexp " \" +width=\"\\([0-9]+\\)\" +height=\"\\([0-9]+\\)\" ?>" nil t)

The toothpick syndrom gets crazy making already difficult regex syntax
impossible to read and hard to code.

My question is, why is elisp's regex has this 2-steps process? Is this
some design decision or just happened that way historically?

Second question: can't elisp create some like “regex-string” wrapper
function that automatically takes care of the quoting? I can't see how
this migth be difficult?

Xah wrote:

If all you want to capture is the x or y (without the square brackets):

"\\[\\([a-z]\\)\\]"

The enclosing double quotes are misleading in this context. I would
simply write (again, capturing the letter but not the brackets):

\[\([a-z]\)\]

On Wed, Jul 09, 2008 at 03:30:27AM -0700, Xah wrote:

Yes. The greatest number of consecutive backslashes I've seen (in a
non-joke context) is 10.

Ironically, Xah, you are doing the same sort of thing in your post,
using crazy quote characters (if that is indeed what they are), 0x5397c
and 0x5397d (according to C-u C-x =). Over my SSH link to my SSP, your
quotes look something like "â~@~]", and are most difficult to read
without a pair of sunspecs which filters out the UTF.

Could you, perhaps, use the standard ASCII quotes 0x22 and 0x27 here,
please?