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Date: Mon, 7 Nov 2016 01:17:45 +0000
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Subject: Re: [RFC] Interval Comparison
From: ajf@ajf.me (Andrea Faulds)

Hi,

Fleshgrinder wrote:
> It is not very readable and repetitive. It would be interesting to
> support a more mathematical notation for this:
>
> ```
> if (0 < $x < 42) {
>      echo 'x is in (0, 42)';
> }
>
> if (0 <= $x <= 42) {
>      echo 'x is in [0, 42]';
> }
> ```
>
> I cannot judge how complicated it is to extend the Bison definitions to
> allow this. However, if there is interest I'm sure there is a way. :)
>

Python supports this, I believe it lets you use arbitrary chains of 
comparisons.

PHP is in the fortunate position where the associativity of the 
comparison operators is undefined. That is, `0 < $x < 42` is currently 
invalid syntax. Some other languages made the (in my view) mistake of 
defining a precedence here, so that it gets interpreted as `(0 < $x) < 
42`, which is (generally?) useless. PHP doesn't have this problem.

I've wanted to do this myself, but figuring out how to implement it was 
tricky, so I didn't spend much time on it. But it's certainly possible, 
and I'd appreciate this if it was added.

Thanks for bringing it up!

-- 
Andrea Faulds
https://ajf.me/