From: Stefano Crocco <stefano.crocco@...>
Date: 2007-11-23T02:49:31+09:00
Subject: Re: Checking whether a string is a number in disguise?

Alle giovedì 22 novembre 2007, Peter Bunyan ha scritto:
> I'm working on an RPN calculator (don't ask why...) and I'm having
> trouble getting a number from gets - how am I supposed to know whether
> it's a number?
>
> At the moment I'm doing [eval(oper) == oper.to_f], which is far from
> ideal. Any ideas? You all get to win my calculator if you know of a
> better way :D.

Do you mean you need to find out whether a string contains a number or not? In 
this case, you can either use Kernel#Float, which returns str.to_f if the 
string contains a number and raises an exception owtherwise, or try to craft 
a regexp which only matches strings containing numbers. For example, the 
(untested) regexp

/[+-]?\d+(.\d+)?(e[+-]?\d+)?/

should match numbers with an optional + or - in front, followed by at least 
one digit, with an optional decimal part (if there's a dot, there should be 
at least one digit following it; if you want to allow something like 11. then 
replace (.\d+) with (.\d*) ). The number can also be in exponential form, 
with a downcase e and an optional + or - in front of the exponent.

I hope this helps

Stefano