An indent-line-function configurator

el-indent allows to quckly build an indent-line-function for a major mode. It may be helpful if you'd like to customize the way code is indented in mode you're using or if you're writing support for a new mode.

Add el-indent.el to you .emacs load-path

To use with a major-mode add (require 'el-indent)

(NOTE: adding to MELPA soon, so these instructions will change.)

Load feature and add hook to your mode, e.g. for lisp-mode:

(require 'el-indent/lisp)
(add-hook 'lisp-mode-hook 'el-indent-set-lisp)

Naming convention for other modes stays the same. For xml-mode will be: el-indent/xml and el-indent-set-xml etc.

To configure indent-line-function you need to provide list of strings that affects indentation.

Example - let's say we deal with mode in which code is nested by parenthesis. So ( nests +1 and ) nests -1, we configure rules this way:

(list
    (list "\(" "\)")
    (list 1    -1)
    (list t    t))

In first list you group strings (in form of regexps) that affect indentation. In second you say which way it affects indentation and in third list you say what rules should be followed after that string in code occured. If it's same rules then you may just put t. otherwise you should put object with differnt rules that would be used afterwards.

Sometimes in first group you'll put string that change the rules of indentation but actually doesn't indent the code. For example beginning of comments might be the case, then just put 0 in second list.

Finally you'll pack rules into functions for direct use:

(setq el-indent-exp-mymode
    (el-indent-build-exps
        (list
            (list "\(" "\)")
            (list 1    -1)
            (list t    t))))

; el-indent-build-exps translates your rules into expressions that are
evaluated when actually indenting.

(defun el-indent-mymode ()
    (el-indent-line (lambda () el-indent-exp-mymode)))

; In place of lambda you may put your custom function that will return different
; expressions according to place in which indent is calculated

(defun el-indent-set-mymode ()
    (setq indent-line-function 'el-indent-mymode))

That's it, configuration may be used as described in How to use ready configurations.

Indent rules are generally more complicated than in this example. You can learn more from configurations that are included with this project.