Re: Parsing beyond sexps

["Mattias Engdegård" <mattiase@acm.org>]

19 jan. 2020 kl. 09.11 skrev Damien Cassou <damien@cassou.me>:

> This is not enough though as I want comments and line/column positions
> in the yielded values. Is there anything I could use from Emacs core
> that would make my life easier?

Nothing in Emacs core that I know of, but you could have a look at how the 'relint' package does it: keep track of the position before each top-level form, and then maintain a path of list indices taken as it descends into each form. Example:

(defun select-weapon (opponent)
  "A Matter of Life and Death."
  (if (fencing-master-p opponent)
      'duelling-pistols
    'rapier))

The path to duelling-pistols would be (1 2 4), since it is built up backwards as a stack during descent: first take element 4 of the top-level form to the 'if'-expression, then element 2 of that form to the (quote duelling-pistols), and finally element 1 to get past the quote. Maintaining the path during traversal turns out to be fairly cheap.

The tuple <top-level-position, path> can then be transformed into <line, column> (or just a buffer position) when required for diagnostics; see 'relint--pos-line-col-from-toplevel-pos-path'. It's somewhat slow but not time-critical.