What is a simple way to combine two Emacs major modes, or to change an existing mode?

Question

In Emacs, I'm working with a file that is a hybrid of two languages.

Question 1: Is there a simple way to write a major mode file that combines two major modes?

Details:

• The language is called "brew" (not the "BREW" of "Binary Runtime Environment for Wireless").

• brew is made up of the languages R and Latex, whose modes are R-mode and latex-mode.

• The R code appears between the tags <% and %>. Everything else is Latex.

• How can I write a brew-mode.el file? (Or is one already available?)

One idea, which I got from this posting, is to use Latex mode, and treat the code of the form <% ... %> as a comment.

Question 2: How do you change the .emacs file or the latex.el file to have Latex mode treat code of the form <% ... %> as a comment?

Answer 1

A number of folks have written solutions enabling you to use multiple major modes at once. See the Emacs Wiki for Multiple Modes. I personally have no experience with them and cannot recommend one over another.

Answer 2

To answer your second question you need to use the font-lock-add-keyword function; give it a major mode to add keywords too, and a association list of regex / face:

(font-lock-add-keywords 'latex-mode
   '(("\<\%.*\%\>" . font-lock-comment-face)))

More details here on emacswiki: http://www.emacswiki.org/emacs/AddKeywords