Re: How to read an integer from the minibuffer

[Yuri Khan]

On Tue, 16 Nov 2021 at 16:38, Emanuel Berg via Users list for the GNU
Emacs text editor <help-gnu-emacs@gnu.org> wrote:

> (defun string-to-number-number (str)
>   (let ((s (string-trim str)))
>     (if (string-match "^[+-]\\{0,1\\}\\(0+\\|0*\\.0+\\)$" s)
>         0
>       (let ((num (string-to-number s)))
>         (when (and (not (zerop num))
>                    (string-match 
> "^[+-]\\{0,1\\}\\([[:digit:]]+\\|[[:digit:]]*\\.[[:digit:]]+\\)$" s) )
>           num) ))))

If you’re checking the input string by regexp anyway, you could do
that before calling the parser and simplify to:

    (defun string-to-number-strict (str)
      (if (string-match
"^[+-]?\\([[:digit:]]+\\|[[:digit:]]*\\.[[:digit:]]+\\)$" s)
          (string-to-number s)
        (error "invalid number")))

(Depending on circumstances, you might want to refine the regexp to
disallow leading zeros unless it is the only digit in the integer
part; and/or allow exponential format. It might also be a good idea to
wrap all that in a ‘save-match-data’.)