如何用Emacs Lisp编写函数实现Haskell语法高亮？

Got it, let's get your Haskell function definition highlighting working in Emacs. The function-based approach is the right call here since Elisp regex doesn't support lookarounds, but there are a few issues in your code that are keeping it from working properly.

First, let's go over the main problems:

• Invalid newline character syntax: In find-equal-character, you wrote ? which is not valid Elisp—newlines need to be written as ?\n. That's probably causing errors right off the bat.
• Inefficient character lookup: Your get-cur-character uses buffer-substring which creates unnecessary strings; we can use char-after directly for better performance and cleaner code.
• Match data preservation: While your logic checks for the equals sign, we need to make sure the match data from the initial regex search stays intact so font-lock knows exactly what text to highlight.

Here's the fixed and improved version of your code:

(defun get-cur-character (pos)
  ;; Grab the character at the given position using char-after (more efficient)
  (char-after (1- pos)))

(defun find-equal-character (pos)
  (let ((curchar nil)
        (result nil)
        (max-pos (point-max)))
    (while (and (not (equal curchar ?\n)) (< pos max-pos))
      (setq curchar (get-cur-character pos))
      (setq pos (1+ pos))
      (when (equal curchar ?=)
        (setq result t)
        (setq curchar ?\n))) ; Exit loop as soon as we find =
    result))

(defun highlight-haskell-function (limit)
  (save-excursion
    (when (re-search-forward "^\\([a-z]+\\w*\\)" limit t)
      ;; Only return true if we found an equals sign after the match
      (when (find-equal-character (match-end 0))
        t)))) ; Match data from re-search-forward is still valid here

;; Make sure we add the keywords after haskell-mode is loaded
(eval-after-load 'haskell-mode
  '(font-lock-add-keywords 'haskell-mode
                            '((highlight-haskell-function . 'font-lock-keyword-face))))

(provide 'haskell-mode)

Let's walk through the changes:

• Fixed newline syntax: Replaced the broken ? with ?\n so Elisp recognizes the newline character correctly.
• Optimized character fetching: get-cur-character now uses char-after, which is faster and avoids creating unnecessary substrings.
• Early loop exit: Once we find the = sign, we set curchar to ?\n to break out of the loop immediately instead of scanning the rest of the line.
• Safe loading: Used eval-after-load to ensure we don't try to modify haskell-mode before it's been loaded into Emacs—this prevents errors on startup.
• Preserved match data: By returning t only when both the regex match and equals sign check pass, we keep the match data from the initial re-search-forward intact. Font-lock uses this match data to know which part of the buffer to apply the face to.

To use this:

1. Save this code in a file (e.g., haskell-function-highlight.el)
2. Add (require 'haskell-function-highlight) to your Emacs config file (init.el or .emacs)
3. Open a Haskell file—any function starting with a lowercase letter (followed by letters, digits, or underscores) with an = on the same line should now be highlighted with the keyword face.

If you want to use a different face (like the standard function name face), just change font-lock-keyword-face to font-lock-function-name-face in the font-lock-add-keywords line.

One quick note: Your current regex ^\\([a-z]+\\w*\\) doesn't match function names with hyphens (like my-cool-function), which are common in Haskell. If you want to support those, adjust the regex to ^\\([a-z][\\w-]*\\)—this allows hyphens in the function name.

内容的提问来源于stack exchange，提问作者user9775773