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|
;;; haskell-tab-indent.el --- tab-based indentation for haskell-mode -*- lexical-binding: t; -*-
;; Copyright (C) 2015, 2017, 2020 Sean Whitton
;; Author: Sean Whitton <spwhitton@spwhitton.name>
;; URL: https://spwhitton.name/tech/code/haskell-tab-indent/
;; Version: 0.3
;; Package-Version: 0.3
;; Keywords: indentation, haskell
;; This file is NOT part of GNU Emacs.
;;; License:
;; 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:
;; This file provides `haskell-tab-indent-mode', a simple indentation
;; mode for Haskell projects which require tabs for indentation and do
;; not permit spaces (except for where clauses, as a special case).
;;
;; The user may use TAB to cycle between possible indentations.
;;
;; Installation:
;;
;; If you set `indent-tabs-mode' in the .dir-locals.el file for a
;; project requiring tabs, you can use something like this in your
;; init file to enable this mode for such projects:
;;
;; (add-hook 'haskell-mode-hook
;; (lambda ()
;; (add-hook 'hack-local-variables-hook
;; (lambda ()
;; (if indent-tabs-mode
;; (haskell-tab-indent-mode 1)
;; (haskell-indentation-mode 1)))
;; nil t))) ; local hook
;;; Code:
(require 'cl-lib)
(require 'seq)
(cl-flet*
((count-line-tabs () (save-excursion
(back-to-indentation)
(length (seq-filter (lambda (c) (equal c ?\t))
(buffer-substring
(line-beginning-position)
(point)))))))
(defun haskell-tab-indent ()
"Auto indentation on TAB for `haskell-tab-indent-mode'."
(interactive)
(let ((this-line-tabs (count-line-tabs))
(prev-line-tabs
(save-excursion
(cl-loop do (beginning-of-line 0)
while (looking-at "[[:space:]]*$"))
(count-line-tabs)))
;; determine whether previous line is a declaration
(prev-line-decl
(save-excursion
(beginning-of-line 0)
(looking-at "[[:space:]]*[^[:space:]]+ ::"))))
(save-excursion
(back-to-indentation)
(if (looking-at "where$")
(setf (buffer-substring (line-beginning-position) (point)) " ")
;; if the previous line is a declaration, then this line
;; should be either empty, or at the same indent level as
;; that declaration
(if prev-line-decl
(setf (buffer-substring (line-beginning-position) (point))
(make-string prev-line-tabs ?\t))
;; check for special case of being called by
;; `newline-and-indent': if the user has `electric-indent-mode'
;; on and RET bound to `newline-and-indent', we'll end up
;; indenting too far, or not enough if the previous line was a
;; declaration
(unless (or
;; avoid indenting too far
(and (equal this-command 'newline-and-indent)
(= this-line-tabs prev-line-tabs)
(not prev-line-decl))
;; avoid indenting too little
(and prev-line-decl (= 1 this-line-tabs)))
(if (>= this-line-tabs (1+ prev-line-tabs))
;; reset
(delete-region (line-beginning-position) (point))
;; indent
(insert "\t")))))))
;; on a line with only indentation, ensure point is at the end
(when (save-excursion (beginning-of-line) (looking-at "[[:space:]]*$"))
(end-of-line))))
;;;###autoload
(define-minor-mode haskell-tab-indent-mode
"Haskell indentation mode for projects requiring that only tabs
-- with no spaces -- be used for indentation.
Binds the TAB key to cycle between possible indents."
:lighter " TabInd"
(kill-local-variable 'indent-line-function)
(when haskell-tab-indent-mode
;; recent `haskell-mode' considers `haskell-indentation-mode' to
;; be the default, and unconditionally turns it on. Follow recent
;; `haskell-indent-mode' and turn it off when activating our mode
(when (and (bound-and-true-p haskell-indentation-mode)
(fboundp 'haskell-indentation-mode))
(haskell-indentation-mode 0))
(set (make-local-variable 'indent-line-function) 'haskell-tab-indent)
(set (make-local-variable 'indent-tabs-mode) t)))
(provide 'haskell-tab-indent)
;;; haskell-tab-indent.el ends here
|
