[[https://www.swi-prolog.org/pldoc/man?section=quasiquotations][library(quasi_quotations) in the SWI-Prolog manual]].
+** Aligning with multiple spaces
+:PROPERTIES:
+:CUSTOM_ID: whitespace
+:END:
+
+#+CINDEX: whitespace
+By convention, if-then-else constructs are aligned such that each goal
+starts at the fourth column after the /start/ of the opening parenthesis
+or operator, as follows:
+
+ #+begin_src prolog
+ ( if
+ -> then
+ ; else
+ ,*-> elif
+ ; true
+ )
+ #+end_src
+
+To simplify maintaining the desired layout without manually counting
+spaces, ~sweep~ provides a command that updates the whitespace around
+point such that the next token is aligned to a (multiple of) four
+columns from the start of the previous token.
+
+#+FINDEX: sweeprolog-align-spaces
+#+FINDEX: cycle-spacing
+To insert or update whitespace around point, use the command ~M-x
+sweeprolog-align-spaces~. For example, consider a ~sweeprolog-mode~
+buffer with the following contents, where =^= designates the location of
+the cursor:
+
+#+begin_src prolog
+ foo :-
+ ( if
+ ;
+ ^
+#+end_src
+
+Calling ~M-x sweeprolog-align-spaces~ will insert three spaces, to yield
+the expected layout:
+
+#+begin_src prolog
+ foo :-
+ ( if
+ ;
+ ^
+#+end_src
+
+In Emacs 29, the command ~M-x cycle-spacing~ is extensible through a
+list of callback functions stored in the variable
+~cycle-spacing-actions~. ~sweep~ leverages this facility and adds
+~sweeprolog-align-spaces~ as the first action of ~cycle-spacing~. To
+inhibit this ~sweeprolog-mode~ from doing so, set the user option
+~sweeprolog-enable-cycle-spacing~ to nil.
+
+Moreover, in Emacs 29 ~cycle-spacing~ is bound by default to ~M-SPC~, thus
+aligning if-then-else and similar constructs only requires typing
+~M-SPC~ after the first token.
+
+In Emacs prior to version 29, users are advised to bind
+~sweeprolog-align-spaces~ to ~M-SPC~ directly by adding the following
+lines to Emacs' initialization file (see [[info:emacs#Init File][The Emacs Initialization File]]).
+
+#+begin_src emacs-lisp
+ (eval-after-load 'sweeprolog
+ '(define-key sweeprolog-mode-map (kbd "M-SPC") #'sweeprolog-align-spaces))
+#+end_src
+
** Term-based editing and motion commands
:PROPERTIES:
:CUSTOM_ID: term-based-commands
of each package.
* Contributing
+:PROPERTIES:
+:CUSTOM_ID: contributing
+:END:
We highly appreciate all contributions, including bug reports,
patches, improvement suggestions, and general feedback.
For a list of known desired improvements in ~sweep~, see [[*Things to do][Things to do]].
** Setting up sweep for local development
+:PROPERTIES:
+:CUSTOM_ID: development-setup
+:END:
Since the Prolog and C parts of ~sweep~ are intended to be distributed
and installed along with SWI-Prolog (see [[#installation][Installation]]), the easiest
#+end_src
** Submitting patches and bug reports
+:PROPERTIES:
+:CUSTOM_ID: submitting-patches
+:END:
The best way to get in touch with the ~sweep~ maintainers is via [[https://lists.sr.ht/~eshel/dev][the
sweep mailing list]].
mailing list.
* Things to do
+:PROPERTIES:
+:CUSTOM_ID: thigs-to-do
+:END:
While ~sweep~ is ready to be used for effective editing of Prolog code,
there some further improvements that we want to pursue:
** Improvements around editing Prolog
+:PROPERTIES:
+:CUSTOM_ID: todo-editing
+:END:
- Inherit user customizations from ~prolog-mode~ :: ~sweep~ should inherit
user customizations from the standard =prolog.el= built into Emacs to
modifications, but careful consideration is required to make sure
~sweeprolog-mode~ overrides all conflicting ~prolog-mode~ features.
-- Provide automatic whitespace formatting for if-then-else constructs :: By
- convention, if-then-else constructs are aligned such that each goal
- starts at the fourth column after the /start/ of the opening
- parenthesis or operator, as follows:
-
- #+begin_src prolog
- ( if
- -> then
- ; else
- ,*-> elif
- ; true
- )
- #+end_src
-
- Note that the number of spaces differs from line to line, e.g. in
- the first line there are three spaces because the opening
- parenthesis in only spans a single column, while the second line
- contains two spaces since the operator ~->~ is already two columns
- long.
-
- ~sweep~ should make it trivial for users to achieve the conventional
- layout without manually counting spaces. Ideally, pressing ~TAB~ or
- ~SPC~, possibly with a modifier, after the opening parenthesis or
- operator should result in the above layout.
-
- Reflect buffer status in the mode line :: It may be useful to
indicate in the mode line whether the current ~sweeprolog-mode~ buffer
has been loaded into the Prolog runtime and/or if its
to matching candidates in the specified module.
** Improvements around running Prolog
+:PROPERTIES:
+:CUSTOM_ID: todo-running
+:END:
- Persist top-level history across sessions :: ~sweep~ should persist
Prolog top-level histories across invocations of
~sweeprolog-top-level~, ideally also across different Emacs sessions.
** General improvements
+:PROPERTIES:
+:CUSTOM_ID: todo-general
+:END:
- Facilitate interactive debugging :: ~sweep~ should facilitate
interactive debugging of SWI-Prolog code. This is a big topic that
we don't currently address. Perhaps this should handled through
;; Maintainer: Eshel Yaron <~eshel/dev@lists.sr.ht>
;; Keywords: prolog languages extensions
;; URL: https://git.sr.ht/~eshel/sweep
-;; Package-Version: 0.5.2
+;; Package-Version: 0.5.3
;; Package-Requires: ((emacs "28"))
;; This file is NOT part of GNU Emacs.
:type '(alist :key-type string :value-type symbol)
:group 'sweeprolog)
+(defcustom sweeprolog-enable-cycle-spacing t
+ "If non-nil and `cycle-spacing-actions' is defined, extend it.
+
+This makes the first invocation of \\[cycle-spacing] in
+`sweeprolog-mode' buffers update whitespace around point using
+`sweeprolog-align-spaces', which see."
+ :package-version '((sweeprolog . "0.5.3"))
+ :type 'boolean
+ :group 'sweeprolog)
+
(defcustom sweeprolog-colourise-buffer-on-idle t
"If non-nil, update highlighting of `sweeprolog-mode' buffers on idle."
:package-version '((sweeprolog . "0.2.0"))
(defvar-local sweeprolog--timer nil)
(defvar-local sweeprolog--colourise-buffer-duration 0.2)
+
+(defun sweeprolog-align-spaces (&optional _)
+ "Adjust in-line whitespace between the previous next Prolog tokens.
+
+This command ensures that the next token starts at a column
+distanced from the beginning of the previous by a multiple of
+four columns, which accommodates the convetional alignment for
+if-then-else constructs in SWI-Prolog."
+ (interactive "" sweeprolog-mode)
+ (let ((bol (line-beginning-position)))
+ (pcase (sweeprolog-last-token-boundaries)
+ (`(,_ ,lbeg ,lend)
+ (when (<= bol lend)
+ (let ((num (- 4 (% (- lend lbeg) 4))))
+ (when (< 0 num)
+ (goto-char lend)
+ (combine-after-change-calls
+ (delete-horizontal-space)
+ (insert (make-string num ? ))))))))))
+
;;;###autoload
(define-derived-mode sweeprolog-mode prog-mode "sweep"
"Major mode for reading and editing Prolog code."
(when sweeprolog-enable-eldoc
(setq-local eldoc-documentation-strategy #'eldoc-documentation-default)
(add-hook 'eldoc-documentation-functions #'sweeprolog-predicate-modes-doc nil t))
+ (when (and (boundp 'cycle-spacing-actions)
+ (consp cycle-spacing-actions)
+ sweeprolog-enable-cycle-spacing
+ (setq-local cycle-spacing-actions (cons #'sweeprolog-align-spaces cycle-spacing-actions))))
(let ((time (current-time)))
(sweeprolog-colourise-buffer)
(setq sweeprolog--colourise-buffer-duration (float-time (time-since time))))
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