Re: compilation-error-regexp-alist syntax problems

[Stefan Monnier <monnier@iro.umontreal.ca>]

>         (cons '("\\[javac\\] *\(/[^:]+\):\([^:]*\):" 1 2) compilation-error-regexp-alist)
                                \\(    \\) \\(   \\)

The regexp is written as a string.  \ is both a string and
a regexp operator.  When you write \n in a string it is turned into
linefeed char.  When you write \( it is turned into an open paren
(i.e. just as if there was no backslash), when you write \\ it is turned
into a single backslash.  To pass \( to the regexp engine, you have thus to
write \\ for the backslash and ( or \( for the open-paren.

When entering a regexp interactively in C-u C-s (for example), it's
different because it is not written as an elisp string so the quoting is
unnecessary.


        Stefan