Everything

php

[RFC] Interval Comparison

php.internals

Fleshgrinder

9 years ago

Validating whether a number is within a closed or open interval is
currently possible only via a construct like the following:

```
if (0 < $x && $x < 42) {
echo 'x is in (0, 42)';
}

if (0 <= $x && $x <= 42) {
echo 'x is in [0, 42]';
}
```

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. :)

--
Richard "Fleshgrinder" Fussenegger

David Rodrigues

9 years ago

I guess that the biggest problem is about the code parsing. Currently PHP
should supports what you wrote, but with another meaning. And personally I
think that this feature is not too common on programming language in
general, once that it is possible from first format (maybe more clear too).

Em 6 de nov de 2016 6:30 PM, "Fleshgrinder" <php@fleshgrinder.com> escreveu:

David Walker

9 years ago

On Sun, Nov 6, 2016 at 1:59 PM David Rodrigues <david.proweb@gmail.com>
wrote:

> I guess that the biggest problem is about the code parsing. Currently PHP
> should supports what you wrote, but with another meaning. And personally I
> think that this feature is not too common on programming language in
> general, once that it is possible from first format (maybe more clear too).
>
> Em 6 de nov de 2016 6:30 PM, "Fleshgrinder" <php@fleshgrinder.com>
> escreveu:
>
> > Validating whether a number is within a closed or open interval is
> > currently possible only via a construct like the following:
> >
> > ```
> > if (0 < $x && $x < 42) {
> >     echo 'x is in (0, 42)';
> > }
> >
> > if (0 <= $x && $x <= 42) {
> >     echo 'x is in [0, 42]';
> > }
> > ```
> >
> > 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]';
> > }
> > ```
> >
>
>

Richard,

I'd be a +1 on this.  I dislike having the double comparison all over
checking for bounds, and have for quite a while. Akin to what David brought
up, https://3v4l.org/7MvlB.  It seems the requested syntax is not valid in
any PHP version testable here.  I can't speak to the complexities of
implementing something like that, but would find it useful.

Of course, you'd have to worry about other conditions like
```
if (0 < $x > 20)
```
By worry about, I mean, should it be invalid syntax, or, should it be
optimized to be `20 < $x`?  I'd say you'd have to maintain the gt/lt for
chaining.

Then I'd wonder about similar syntax to check if 2 variables are both
greater than 0, but one greater/equal to the other:
```
if (0 < $x <= $y)
```

--
Dave

Andrew Faulds

9 years ago

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/