I have a source file that was originally coded in TeX (well, this is actually a conTeXt file). A fraction like 1/(2/x^2) is coded as {1 \over {2 \over x^2}}. I'd like to convert to LaTeX syntax, that is \frac{1}{\frac{2}{x^2}}.
Any hints? Thanks.
The command my-replace-over-with-frac defined in the following Elisp code assumes that \over arguments are always delimited by braces.
There are more constructs that limit the arguments of \over like $ a \over b $ $ c \over d $ or $\matrix{ a \over b & c \over d }$. In each of those cases a \over b and c \over d are rendered as separate fractions.
If one ignores that it may lead to an invalid LaTeX document.
For that reason the default application of my-replace-over-with-frac is interactive by default. For each match of \over you are asked whether you want to accept the replacement or not. The text modifications are marked with yellow color.
If you skip some replacements you can afterwards search for \over to find those cases and edit them.
If you are venturesome you can call my-replace-over-with-frac with prefix-arg. In that case all replacements are done without user-interaction.
(defun my-next-over (&rest args)
"Search for the next \\over in a math environment.
ARGS are the arguments starting at the 2nd one of `search-forward'."
(cl-loop while (apply #'search-forward "\\over" args)
when (and (save-match-data (texmathp))
(null (nth 8 (syntax-ppss (point)))))
return (point)
finally return nil))
(defun my-replace-over-with-frac (&optional b e force)
"Replace {a \\over b} with {\frac{a}{b}} in region from B to E.
Make replacements without questions if FORCE is non-nil.
Thereby, a and b can be terms that can contain fractions themselves."
(interactive (append
(if (use-region-p)
(list (region-beginning) (region-end))
(list nil nil))
(list prefix-arg)))
(save-point
(unless b (setq b (point-min)))
(unless e (setq e (point-max)))
(goto-char b)
(let ((ol-over (make-overlay 1 1))
(ol-frac (make-overlay 1 1))
(ol-brace (make-overlay 1 1)))
(unwind-protect
(progn
(overlay-put ol-over 'face 'match)
(overlay-put ol-frac 'face 'match)
(while (my-next-over e t)
(move-overlay ol-over (match-beginning 0) (match-end 0))
(replace-match "}{")
(goto-char (match-beginning 0))
(backward-up-list)
(let ((b-frac (point)))
(insert "{\\frac")
(move-overlay ol-frac b-frac (point)))
(forward-sexp 2)
(insert "}")
(move-overlay ol-brace (1- (point)) (point))
(if (or force
(y-or-n-p "Apply? "))
(goto-char (overlay-end ol-over)) ;; consider other occurences of \over in the second operand
(delete-region (overlay-start ol-over) (overlay-end ol-over))
(goto-char (overlay-start ol-over))
(insert "\\over")
(save-point
(delete-region (overlay-start ol-frac) (overlay-end ol-frac))
(delete-region (overlay-start ol-brace) (overlay-end ol-brace))))
)
)
(delete-overlay ol-over)
(delete-overlay ol-frac)
(delete-overlay ol-brace)))))
(delete-overlay ol-frac)))))
The interaction stuff hides a bit the simplicity of the method.
The structure of the method is:
(while (search-forward "\\over")
(save-point
(replace-match "}{")
(backward-up-list)
(insert "\\frac")))
The following code replaces {1 \over {2 \over x^2}} with \frac{1}{\frac{2}{x^2}}.
(save-excursion
(goto-char (point-min))
(while (re-search-forward
"{\\([0-9]*\\)\s\\\\over\s{\\([0-9]*\\)\s\\\\over\s\\([^}]*\\)}}" nil t)
(replace-match "\\\\frac{\\1}{\\\\frac{\\2}{\\3}}")))
I believe you may be looking for the function replace-string, or replace-regexp. These let you enter a before (frac) and after (over) and replaces found occurrences.
Here is documentation: https://www.gnu.org/software/emacs/manual/html_node/emacs/Regexp-Replace.html
If you want to go one by one to make sure that what you're changing should be changed (perhaps an instance where you want to change some, but not all), you want query-replace-regexp.
Here is documentation for that: https://www.gnu.org/software/emacs/manual/html_node/emacs/Query-Replace.html
