Question

How to check whether the character before point equals “\“

(defun comment-latex () 
  (interactive)
  (if (region-active-p) 
      (comment-region (region-beginning) (region-end))
     (if (= (char-before) ("\\")                 ;; how to fix this sentence?     
       (insert "%")
      (if (= (point) (line-beginning-position)) ;; this part works
        (insert "% ")
       (end-of-line)
       (insert " % "))))
)
(global-set-key LaTeX-mode-map (kbd "%") 'comment-latex)

The code as example should be doing the following:

1) If a region is selected, the region should be commented.

2) If the character before point is a “\“, a normal % should be inserted at point.

3) If point is at the beginning of line, insert a “%”

4) If point is anywhere else, go to the end of the sentence and insert “SPC % SPC“

Answer 1

The syntax for individual characters is ?char. So:

(= (char-before) ?\\)