Re: Determining validity of mathematical expression before evaluation

On Friday, March 27th, 2026 at 12:42 PM, Heime <[email protected]> wrote:

> Is it possible to determine whether an elisp mathematical expression
> is valid before evaluating it?

Have tried this, passing a string expression and evaluating it.
And if it fails, I call bc.  But have not been capable of using
condition-case properly.

(defun calc (expr)
  "Evaluate arithmetic expression interactively.
Enter operation and numbers as a single string like: '10 + 5 * 2'."
  (interactive "sExpression (10 + 5 * 2): ")

  (condition-case err
      (let ((result (eval (read expr))))
	(message "Result (eval): %s" result))

    (progn 
      (string-to-number 
       (shell-command-to-string 
	(format "echo '%s' | bc -l" expr)))
      (message "Result (bc): %s" result))))