1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
|
;;; 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))))))
(line-first-word () (save-excursion
(back-to-indentation)
(let ((beg (point)))
(while (not (looking-at "[[:space:]]"))
(forward-char))
(buffer-substring-no-properties beg (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:]]*$"))
(count-line-tabs)))
(this-first-word (line-first-word))
(prev-first-word (save-excursion
(beginning-of-line 0)
(line-first-word)))
;; determine whether previous line is a declaration
(prev-line-decl
(save-excursion
(beginning-of-line 0)
(looking-at "[[:space:]]*[^[:space:]]+ ::"))))
(save-excursion
(back-to-indentation)
(if (looking-at "where$")
(setf (buffer-substring (line-beginning-position) (point)) " ")
;; attempt to line up declarations and definitions
(if (and prev-line-decl
(string= this-first-word prev-first-word))
(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
|
