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;;; haskell-simple-indent.el --- Simple indentation module for Haskell Mode
;; Copyright (C) 1998 Heribert Schuetz, Graeme E Moss
;; Author: Heribert Schuetz <Heribert.Schuetz@informatik.uni-muenchen.de>
;; Graeme E Moss <gem@cs.york.ac.uk>
;; Keywords: indentation files Haskell
;; 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 3, 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 this program. If not, see <http://www.gnu.org/licenses/>.
;;; 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.)
;;; Code:
;; All functions/variables start with
;; `(turn-(on/off)-)haskell-simple-indent'.
(require 'haskell-mode)
(defgroup haskell-simple-indent nil
"Simple Haskell indentation."
:link '(custom-manual "(haskell-mode)Indentation")
:group 'haskell
:prefix "haskell-simple-indent-")
;; Version.
(defconst haskell-simple-indent-version "1.2"
"`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. Example:
func arg cx = when (isTrue) $ do
print 42
^ ^ ^ ^ ^ ^ ^ ^ ^ ^
A position is visible if it is to the left of the first
non-whitespace (indentation) of every nonblank line between the
position and the current line. If there is no visible indent
point beyond the current column, position given by
`indent-next-tab-stop' is used instead."
(interactive)
(let* ((start-column (or (save-excursion
(back-to-indentation)
(if (not (eolp))
(current-column)))
(current-column)))
(invisible-from nil) ; `nil' means infinity here
(found)
(indent))
(save-excursion
;; Loop stops if there no more lines above this one or when has
;; found a line starting at first column.
(while (and (not found)
(or (not invisible-from)
(not (zerop invisible-from)))
(zerop (forward-line -1)))
;; Ignore empty lines.
(if (not (looking-at "[ \t]*\n"))
(let ((this-indentation (current-indentation)))
;; Is this line so indented that it cannot have
;; influence on indentation points?
(if (or (not invisible-from)
(< this-indentation invisible-from))
(if (> this-indentation start-column)
(setq invisible-from this-indentation)
(let ((end (line-end-position)))
(move-to-column start-column)
;; Is start-column inside a tab on this line?
(if (> (current-column) start-column)
(backward-char 1))
;; Skip to the end of non-whitespace.
(skip-chars-forward "^ \t" end)
;; Skip over whitespace.
(skip-chars-forward " \t" end)
;; Indentation point found if not at the end of
;; line and if not covered by any line below
;; this one. In that case use invisible-from.
(setq indent (if (or (= (point) end)
(and invisible-from
(> (current-column) invisible-from)))
invisible-from
(current-column)))
;; Signal that solution is found.
(setq found t))))))))
(let ((opoint (point-marker)))
;; Indent to the calculated indent or last know invisible-from
;; or use tab-to-tab-stop. Try hard to keep cursor in the same
;; place or move it to the indentation if it was before it. And
;; keep content of the line intact.
(setq indent (or indent
invisible-from
(if (fboundp 'indent-next-tab-stop)
(indent-next-tab-stop start-column))
(let ((tabs tab-stop-list))
(while (and tabs (>= start-column (car tabs)))
(setq tabs (cdr tabs)))
(if tabs (car tabs)))
(* (/ (+ start-column tab-width) tab-width) tab-width)))
(indent-line-to indent)
(if (> opoint (point))
(goto-char opoint))
(set-marker opoint nil))))
(defun haskell-simple-indent-backtab ()
"Indent backwards. Dual to `haskell-simple-indent'."
(interactive)
(let ((saved-column (or (save-excursion
(back-to-indentation)
(if (not (eolp))
(current-column)))
(current-column)))
(i 0)
(x 0))
(save-excursion
(back-to-indentation)
(delete-region (line-beginning-position) (point)))
(while (< (or (save-excursion
(back-to-indentation)
(if (not (eolp))
(current-column)))
(current-column)) saved-column)
(haskell-simple-indent)
(setq i (+ i 1)))
(save-excursion
(back-to-indentation)
(delete-region (line-beginning-position) (point)))
(while (< x (- i 1))
(haskell-simple-indent)
(setq x (+ x 1)))))
(defun haskell-simple-indent-newline-same-col ()
"Make a newline and go to the same column as the current line."
(interactive)
(let ((point (point)))
(let ((start-end
(save-excursion
(let* ((start (line-beginning-position))
(end (progn (goto-char start)
(search-forward-regexp
"[^ ]" (line-end-position) t 1))))
(when end (cons start (1- end)))))))
(if start-end
(progn (newline)
(insert (buffer-substring-no-properties
(car start-end) (cdr start-end))))
(newline)))))
(defun haskell-simple-indent-newline-indent ()
"Make a newline on the current column and indent on step."
(interactive)
(haskell-simple-indent-newline-same-col)
(insert (make-string haskell-indent-spaces ? )))
(defun haskell-simple-indent-comment-indent-function ()
"Haskell version of `comment-indent-function'."
;; This is required when filladapt is turned off. Without it, when
;; filladapt is not used, comments which start in column zero
;; cascade one character to the right
(save-excursion
(beginning-of-line)
(let ((eol (line-end-position)))
(and comment-start-skip
(re-search-forward comment-start-skip eol t)
(setq eol (match-beginning 0)))
(goto-char eol)
(skip-chars-backward " \t")
(max comment-column (+ (current-column) (if (bolp) 0 1))))))
;;;###autoload
(define-minor-mode haskell-simple-indent-mode
"Simple Haskell indentation mode that uses simple heuristic.
In this minor mode, `indent-for-tab-command' (bound to <tab> by
default) will move the cursor to the next indent point in the
previous nonblank line, whereas `haskell-simple-indent-backtab'
\ (bound to <backtab> by default) will move the cursor the
previous indent point. An indent point is a non-whitespace
character following whitespace.
Runs `haskell-simple-indent-hook' on activation."
:lighter " Ind"
:group 'haskell-simple-indent
:keymap '(([backtab] . haskell-simple-indent-backtab))
(set (make-local-variable 'comment-indent-function) #'haskell-simple-indent-comment-indent-function)
(kill-local-variable 'indent-line-function)
(when haskell-simple-indent-mode
(set (make-local-variable 'indent-line-function) 'haskell-simple-indent)
(run-hooks 'haskell-simple-indent-hook)))
;; The main functions.
;;;###autoload
(defun turn-on-haskell-simple-indent ()
"Turn on function `haskell-simple-indent-mode'."
(interactive)
(haskell-simple-indent-mode))
(defun turn-off-haskell-simple-indent ()
"Turn off function `haskell-simple-indent-mode'."
(interactive)
(haskell-simple-indent-mode 0))
;; Provide ourselves:
(provide 'haskell-simple-indent)
;;; haskell-simple-indent.el ends here
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