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bug#59531: 29.0.50: An alternative to `string-to-number` which throws an
From: |
Jean Louis |
Subject: |
bug#59531: 29.0.50: An alternative to `string-to-number` which throws an error (or returns a NIL value) when input is non-parseable as number |
Date: |
Thu, 24 Nov 2022 13:08:20 +0300 |
User-agent: |
Mutt/2.2.7+37 (a90f69b) (2022-09-02) |
* Ramesh Nedunchezian <rameshnedunchezian@outlook.com> [2022-11-24 09:22]:
> `string-to-number` returns ZERO if the input is not a number.
>
>
> This return value is not very helpful. The choice of a number ZERO as "Not A
> Number" doesn't help one to distinguish between the following two cases
>
> (1) Input was a valid number, and it parses to number zero
>
> (2) Input was NOT a valid number, and it was forcibly reported as ZERO
>
> Consider amending `string-to-number` to throw an error (or return NIL) when
> the input is not parseable as a number, or providing an alternative API to
> validate numbers. I am trying to parse some fields in an org table, and see
> if the field value is a number or not;
>
> If there is already an alternative to what I am trying to
> accomplish, I would appreciate a recipe.
I had the same problem, so I have solved it this way.
(defun string-is-number-p (s)
"Return number only if string is actual number, otherwise NIL."
(let* ((s (string-trim s)))
(cond ((seq-empty-p s) nil)
((string-match "[^0123456789\\.-]" s) nil)
((string-match "-" s 1) nil)
((numberp (string-to-number s)) (string-to-number s)))))
As in my case I liketo know that string is really representing number
and nothing else.
(string-is-number-p "Hello") ➜ nil
(string-is-number-p "") ➜ nil
(string-is-number-p "0") ➜ 0
(string-is-number-p "0a") ➜ nil
(string-to-number "0a") ➜ 0
(string-is-number-p "0.1") ➜ 0.1
(string-is-number-p "-2.5121212") ➜ -2.5121212
My function may not be perfect.
--
Jean
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