Emacs: Make elisp-index-search use Current Symbol

By Xah Lee. Date: 2009-01-17. Last updated: 2012-03-25.

Emacs's elisp-index-search command does not use the current symbol when called. This page shows code that fixes that, and also offer some other suggestions.

In emacs, you can press Ctrl+h f to see any emacs lisp function's doc string, and if the cursor is on a function, it defaults to lookup that function. This integrated facility is extremely convenient. However, some improvement can be made. Here are some suggestions:

① Make elisp-index-search's default prompt to be the word under cursor. This seems useful and consistent with other emacs lookup commands.
② Make describe-function's result display a link to the elisp manual's node on that function.
③ Make describe-function's result display related functions as in “See also: …”
④ Extend describe-function so that it is not just for emacs lisp, but for any language as determined by the current mode.

Make elisp-index-search prompt Default to Current Symbol

Kevin Rodgers and others have suggested implementations. (Source groups.google.com) Here's one that works for me:

;; Kevin Rodgers [kevin.d.rodg…@gmail.com], 2008-10-09
(defadvice elisp-index-search (before interactive-default activate)
  "Provide the symbol at point as the default when reading TOPIC interactively."
  (interactive
   (let ((symbol-at-point (thing-at-point 'symbol)))
     (list (read-string (if symbol-at-point
                            (format "Topic (%s): " symbol-at-point)
                          (format "Topic: "))
                        nil nil symbol-at-point)))))

Link to Emacs Manual

Showing a link to elisp manual of pertinent page would be convenient. Because sometimes doc string is not detailed enough or doesn't provide context.

Link to Related Functions

Listing similar functions is a practical need. For example:

search-forward: See also: search-forward-regexp, skip-chars-forward, looking-at.
find-file: See also: with-temp-buffer, with-temp-file.
mapcar: See also: mapc.
beginning-of-line: See also: line-beginning-position, move-beginning-of-line, previous-line.

Listing related functions in a function's doc is in many programing lang manuals. e.g Mathematica, Microsoft's JScript, PHP. They are quite useful. Because, for those who are not yet expert of a language (which is majority), often they do not know similar functions or do not know if there's manual page that list such, and often are confused about the differences of many functions that seem the same. By providing a list of similar functions, a coder can easily locate the right function he need.

Note: some of the above suggestions are reported to emacs dev as bugs: bug#575, bug#1119.

Make describe-function Work for All Popular Languages

Extend describe-function to other languages than emacs lisp, would be a major improvement. For example, in Perl, to lookup a function, i have to type Meta+! perldoc -f function_name Enter. To look up a function while coding in Python, i typically have to switch to shell, start Python interactive interpreter, type “help()” then the function's name. To lookup PHP keywords, i have to switch to browser then type “http://php.net/keyword”. Emacs can automate all these. When describe-function is called, it can simply check the value of “major-mode” local variable to determine the current language, then, switch to web browser with a appropriate URL for that function's doc. If the language's documentation does provide a info format, then the integration would be seamless. (for a proof of concept, see: Emacs: Lookup Google, Dictionary, Documentation.)

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