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;;; haskell-simple-indent.el --- Simple indentation module for Haskell Mode
;; Copyright 1998 Heribert Schuetz, Graeme E Moss
;; Authors:
;; 1998 Heribert Schuetz <Heribert.Schuetz@informatik.uni-muenchen.de> and
;; Graeme E Moss <gem@cs.york.ac.uk>
;; Keywords: indentation files Haskell
;; Version: 1.0
;; URL: http://www.cs.york.ac.uk/~gem/haskell-mode/simple-indent.html
;;; This file is not part of GNU Emacs.
;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;; This file is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING. If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;; Purpose:
;;
;; To support simple indentation of Haskell scripts.
;;
;;
;; Installation:
;;
;; To bind TAB to the indentation command for all Haskell buffers, add
;; this to .emacs:
;;
;; (add-hook 'haskell-mode-hook 'turn-on-haskell-simple-indent)
;;
;; Otherwise, call `turn-on-haskell-simple-indent'.
;;
;;
;; Customisation:
;;
;; None supported.
;;
;;
;; History:
;;
;; If you have any problems or suggestions, after consulting the list
;; below, email gem@cs.york.ac.uk quoting the version of you are
;; using, the version of emacs you are using, and a small example of
;; the problem or suggestion.
;;
;; Version 1.0:
;; Brought over from Haskell mode v1.1.
;;
;; Present Limitations/Future Work (contributions are most welcome!):
;;
;; (None so far.)
;;; All functions/variables start with
;;; `(turn-(on/off)-)haskell-simple-indent'.
;; Version.
(defconst haskell-simple-indent-version "1.1"
"`haskell-simple-indent' version number.")
(defun haskell-simple-indent-version ()
"Echo the current version of `haskell-simple-indent' in the minibuffer."
(interactive)
(message "Using haskell-simple-indent version %s"
haskell-simple-indent-version))
;; Partly stolen from `indent-relative' in indent.el:
(defun haskell-simple-indent ()
"Space out to under next visible indent point.
Indent points are positions of non-whitespace following whitespace in
lines preceeding point. A position is visible if it is to the left of
the first non-whitespace of every nonblank line between the position and
the current line. If there is no visible indent point beyond the current
column, `tab-to-tab-stop' is done instead."
(interactive)
(let ((start-column (current-column))
(invisible-from nil) ; `nil' means infinity here
indent )
(catch 'haskell-simple-indent-break
(save-excursion
(while (progn (beginning-of-line)
(> (point) (point-min)))
(forward-line -1)
(if (not (looking-at "[ \t]*\n"))
(let ((this-indentation (current-indentation)))
(if (or (not invisible-from)
(< this-indentation invisible-from))
(if (> this-indentation start-column)
(setq invisible-from this-indentation)
(let ((end (save-excursion (forward-line 1) (point))))
(move-to-column start-column)
;; Is start-column inside a tab on this line?
(if (> (current-column) start-column)
(backward-char 1))
(or (looking-at "[ \t]")
(skip-chars-forward "^ \t" end))
(skip-chars-forward " \t" end)
(let ((col (current-column)))
(setq indent
(if (or (= (point) end)
(and invisible-from
(> col invisible-from)))
invisible-from
col ) ) )
(throw 'haskell-simple-indent-break nil)))))))))
(if indent
(let ((opoint (point-marker)))
(delete-region (point) (progn (skip-chars-backward " \t") (point)))
(indent-to indent 0)
(if (> opoint (point))
(goto-char opoint))
(move-marker opoint nil))
(tab-to-tab-stop)) ) )
;; The main functions.
(defun turn-on-haskell-simple-indent ()
"Sets `indent-line-function' to `haskell-simple-indent'---a simple
indentation function. Ensures TAB is bound to
`indent-for-tab-command', and LFD to `newline-and-indent'. TAB will
now move the cursor to the next indent point in the previous nonblank
line. An indent point is a non-whitespace character following
whitespace.
Invokes `haskell-simple-indent-hook' if not nil.
Use `haskell-simple-indent-version' to find out what version this is."
(interactive)
(make-local-variable 'haskell-simple-indent-old)
(setq haskell-simple-indent-old indent-line-function)
(make-local-variable 'indent-line-function)
(setq indent-line-function 'haskell-simple-indent)
(local-set-key "\t" 'indent-for-tab-command)
(local-set-key "\n" 'newline-and-indent)
(run-hooks 'haskell-simple-indent-hook))
(defun turn-off-haskell-simple-indent ()
"Returns `indent-line-function' to original value, before
`turn-on-haskell-simple-indent' was called. Leaves TAB and LFD bound
to `indent-for-tab-command' and `newline-and-indent' respectively."
(interactive)
(if (boundp 'haskell-simple-indent-old)
(setq indent-line-function haskell-simple-indent-old)))
;;; Provide ourselves:
(provide 'haskell-simple-indent)
;;; haskell-simple-indent ends here.
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