How to run a command with 'modify-syntax-entry' reset?

Question

I have used modify-syntax-entry to remove underscores from being delimiting characters. e.g:

(modify-syntax-entry ?_ "w")

However I would like to temporary allow underscores to be used as a delimiter.

Normally I would temporarily override a variable with let in a function.

How can the syntax table be temporarily overridden?

Answer 1

You can create a new syntax table, then run the command in a with-syntax-table block:

This is an example of delete forward/backward word, with a modified syntax table.

(defun kill-word-sans-delimiter-impl (arg)
  (let ((table (make-syntax-table)))
    (dolist (ch (list ?- ?_))
      (modify-syntax-entry ch "_" table))
    (with-syntax-table table (kill-word arg))))

(defun kill-word-backward-sans-delimiter (arg)
  (interactive "p")
  (kill-word-sans-delimiter-impl (- arg)))

(defun kill-word-forward-sans-delimiter (arg)
  (interactive "p")
  (kill-word-sans-delimiter-impl arg))