124 lines
5.1 KiB
Markdown
124 lines
5.1 KiB
Markdown
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title: Ligature Emulation in Emacs
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date: 2017-05-04
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Monday was (yet another)
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[NixOS hackathon][hackathon] at [OpenLab Augsburg][ola].
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[Maximilian][mhuber] was there and to my amazement
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he got working ligatures in his Haskell files in Emacs! Ever since Hasklig
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updated its format to use ligatures and private Unicode code points a while ago,
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the hack I had used in my config stopped working.
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Encouraged by that I decided to take a look on Tuesday. Long story short, I was
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able to [get it working in a pretty satisfying way][done].
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[hackathon]: https://www.meetup.com/Munich-NixOS-Meetup/events/239077247/
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[mhuber]: https://github.com/maximilianhuber
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[ola]: https://openlab-augsburg.de
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[done]: https://github.com/i-tu/Hasklig/issues/84#issuecomment-298803495
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What’s left to do is package it into a module and push to melpa.
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### elisp still sucks, but it’s bearable, sometimes
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I’m the kind of person who, when trying to fix something elisp related, normally
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gives up two hours later and three macro calls deep. Yes, homoiconic,
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non-lexically-scoped, self-rewriting code is not exactly my fetish.
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This time the task and the library (`prettify-symbols-mode`) were simple enough
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for that to not happen.
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Some interesting technical trivia:
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- elisp literal character syntax is `?c`. `?\t` is the tab character
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- You join characters by `(string c1 c2 c3 ...)`
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- [dash.el][dash] is pretty awesome and does what a functional programmer
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expects. Also, Rainbow Dash.
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- Hasklig and FiraCode multi-column symbols actually [only occupy one column, on
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the far right of the glyph][glyph]. `my-correct-symbol-bounds` fixes emacs’
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rendering in that case.
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[dash]: https://github.com/magnars/dash.el
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[glyph]: https://github.com/tonsky/FiraCode/issues/211#issuecomment-239082368
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## Appendix A
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For reference, here’s the complete code as it stands now. Feel free to paste
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into your config; let’s make it [MIT][mit]. Maybe link to this site, in case there are
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updates.
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[mit]: https://opensource.org/licenses/MIT
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```elisp
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(defun my-correct-symbol-bounds (pretty-alist)
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"Prepend a TAB character to each symbol in this alist,
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this way compose-region called by prettify-symbols-mode
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will use the correct width of the symbols
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instead of the width measured by char-width."
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(mapcar (lambda (el)
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(setcdr el (string ?\t (cdr el)))
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el)
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pretty-alist))
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(defun my-ligature-list (ligatures codepoint-start)
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"Create an alist of strings to replace with
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codepoints starting from codepoint-start."
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(let ((codepoints (-iterate '1+ codepoint-start (length ligatures))))
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(-zip-pair ligatures codepoints)))
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; list can be found at https://github.com/i-tu/Hasklig/blob/master/GlyphOrderAndAliasDB#L1588
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(setq my-hasklig-ligatures
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(let* ((ligs '("&&" "***" "*>" "\\\\" "||" "|>" "::"
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"==" "===" "==>" "=>" "=<<" "!!" ">>"
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">>=" ">>>" ">>-" ">-" "->" "-<" "-<<"
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"<*" "<*>" "<|" "<|>" "<$>" "<>" "<-"
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"<<" "<<<" "<+>" ".." "..." "++" "+++"
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"/=" ":::" ">=>" "->>" "<=>" "<=<" "<->")))
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(my-correct-symbol-bounds (my-ligature-list ligs #Xe100))))
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;; nice glyphs for haskell with hasklig
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(defun my-set-hasklig-ligatures ()
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"Add hasklig ligatures for use with prettify-symbols-mode."
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(setq prettify-symbols-alist
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(append my-hasklig-ligatures prettify-symbols-alist))
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(prettify-symbols-mode))
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(add-hook 'haskell-mode-hook 'my-set-hasklig-ligatures)
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```
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## Appendix B (Update 1): FiraCode integration
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I also created a mapping for [FiraCode][fira]. You need to grab the [additional
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symbol font][symbol] that adds (most) ligatures to the unicode private use area.
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Consult your system documentation on how to add it to your font cache.
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Next add `"Fira Code"` and `"Fira Code Symbol"` to your font preferences. Symbol
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only contains the additional characters, so you need both.
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If you are on NixOS, the font package should be on the main branch shortly, [I
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added a package][symbol-pkg].
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[fira]: https://github.com/tonsky/FiraCode/
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[symbol]: https://github.com/tonsky/FiraCode/issues/211#issuecomment-239058632
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[symbol-pkg]: https://github.com/NixOS/nixpkgs/pull/25517
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Here’s the mapping adjusted for FiraCode:
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```elisp
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(setq my-fira-code-ligatures
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(let* ((ligs '("www" "**" "***" "**/" "*>" "*/" "\\\\" "\\\\\\"
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"{-" "[]" "::" ":::" ":=" "!!" "!=" "!==" "-}"
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"--" "---" "-->" "->" "->>" "-<" "-<<" "-~"
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"#{" "#[" "##" "###" "####" "#(" "#?" "#_" "#_("
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".-" ".=" ".." "..<" "..." "?=" "??" ";;" "/*"
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"/**" "/=" "/==" "/>" "//" "///" "&&" "||" "||="
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"|=" "|>" "^=" "$>" "++" "+++" "+>" "=:=" "=="
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"===" "==>" "=>" "=>>" "<=" "=<<" "=/=" ">-" ">="
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">=>" ">>" ">>-" ">>=" ">>>" "<*" "<*>" "<|" "<|>"
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"<$" "<$>" "<!--" "<-" "<--" "<->" "<+" "<+>" "<="
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"<==" "<=>" "<=<" "<>" "<<" "<<-" "<<=" "<<<" "<~"
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"<~~" "</" "</>" "~@" "~-" "~=" "~>" "~~" "~~>" "%%"
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"x" ":" "+" "+" "*")))
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(my-correct-symbol-bounds (my-ligature-list ligs #Xe100))))
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```
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