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From: Jean Louis <bugs@gnu.support>
To: Ramesh Nedunchezian <rameshnedunchezian@outlook.com>
Cc: 59531@debbugs.gnu.org
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	[thread overview]
Message-ID: <Y39ClKVhCCwHuRzW@protected.localdomain> (raw)
In-Reply-To: <TY2PR0101MB3693F7DD75CC1CCBA0EB9543DA0F9@TY2PR0101MB3693.apcprd01.prod.exchangelabs.com>

* 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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      parent reply	other threads:[~2022-11-24 10:08 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-24  6:14 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 Ramesh Nedunchezian
2022-11-24  8:00 ` Eli Zaretskii
2022-12-14 16:40   ` Robert Pluim
2022-12-16  6:28     ` Jean Louis
2022-11-24 10:08 ` Jean Louis [this message]

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