ligatures.el

;; Font Ligatures
  (defun my-correct-symbol-bounds (pretty-alist)
      "Prepend a TAB character to each symbol in this alist,
  this way compose-region called by prettify-symbols-mode
  will use the correct width of the symbols
  instead of the width measured by char-width."
      (mapcar (lambda (el)
                (setcdr el (string ?\t (cdr el)))
                el)
              pretty-alist))

  (defun my-ligature-list (ligatures codepoint-start)
      "Create an alist of strings to replace with
  codepoints starting from codepoint-start."
      (let ((codepoints (-iterate '1+ codepoint-start (length ligatures))))
        (-zip-pair ligatures codepoints)))

  (setq my-fira-code-ligatures
      (let* ((ligs '("www" "**" "***" "**/" "*>" "*/" "\\\\" "\\\\\\"
                    "{-" "[]" "::" ":::" ":=" "!!" "!=" "!==" "-}"
                    "--" "---" "-->" "->" "->>" "-<" "-<<" "-~"
                    "#{" "#[" "##" "###" "####" "#(" "#?" "#_" "#_("
                    ".-" ".=" ".." "..<" "..." "?=" "??" ";;" "/*"
                    "/**" "/=" "/==" "/>" "//" "///" "&&" "||" "||="
                    "|=" "|>" "^=" "$>" "++" "+++" "+>" "=:=" "=="
                    "===" "==>" "=>" "=>>" "<=" "=<<" "=/=" ">-" ">="
                    ">=>" ">>" ">>-" ">>=" ">>>" "<*" "<*>" "<|" "<|>"
                    "<$" "<$>" "<!--" "<-" "<--" "<->" "<+" "<+>" "<="
                    "<==" "<=>" "<=<" "<>" "<<" "<<-" "<<=" "<<<" "<~"
                    "<~~" "</" "</>" "~@" "~-" "~=" "~>" "~~" "~~>" "%%"
                    "x" ":" "+" "+" "*")))
        (my-correct-symbol-bounds (my-ligature-list ligs #Xe100))))

  (defun my-set-fira-code-ligatures ()
      "Add fira code ligatures for use with prettify-symbols-mode."
      (setq prettify-symbols-alist
            (append my-fira-code-ligatures prettify-symbols-alist))
      (prettify-symbols-mode))

  (add-hook 'prog-mode-hook 'my-set-fira-code-ligatures)
  )