[RFC] Interval Comparison

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]';
}

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

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/

On Mon, Nov 7, 2016 at 1:38 PM Fleshgrinder php@fleshgrinder.com
wrote:

We are only extending binary to ternary for <= and <.

I realize that my comment, and question were going a bit off-topic with
going on about the chaining of comparisons, but I'm interested in it
more
because I wonder which would be harder to implement. It would seem to
me
that it would be harder to implement a means in which you only allow
one
additional layer of comparison, rather than abstract chaining of
comparisons (<, <=, >, >=).

I'm pretty sure that a three-part comparison is easier to implement. It
can be kind of hard-coded as a new type of syntax, somewhat like the
ternary operator.

Personally I'd prefer the full Python-style chaining. It's a lot more
useful, especially for cases like 0 < $a <= $b < $upper_limit.

One possible implementation idea (not knowing anything about Zend):
Comparison (a<b) would return a pair of data, the result and the latter
value. If this was the last comparison or the result was false, the
value will be dropped and the comparison ends. Else the result (true)
will be dropped and the comparison will go on.

--
Lauri Kenttä

Sense be damed ;-) . I'd attribute it to an identity of sorts (if it was
to go all out with comparison chaining). Yes it makes little sense, in
practice, but the truth of it would be the same.

I realize that my comment, and question were going a bit off-topic with
going on about the chaining of comparisons, but I'm interested in it
more because I wonder which would be harder to implement. It would seem
to me that it would be harder to implement a means in which you only
allow one additional layer of comparison, rather than abstract chaining
of comparisons (<, <=, >, >=). As Andrea noted, python does allow for
arbitrary chains of comparison. I'm not exactly sure how precedence
would work with comparisons, rather, as I see it the comparison would
need to be expanded such

if (0 < $a < $b > 10)

would be akin to

if (0 < $a && $a < $b && $b > 10)

I, of course, am only projecting a potential syntax, and I'm no yacc/ast
aficionado by any metric, but it'd seem to me that it'd be possible to
convert some stack of elements here into a recursive comparison.

This requires associativity, as Python has it.

https://docs.python.org/3/reference/expressions.html#comparisons

The problem, as explained in the Python reference, is that in x < y < z the variables x and z are never compared against each other.
This, however, works great almost always and nothing is wrong in doing
so in my opinion.

That change would actually be brutally easy since we only need to change
the %nonassoc to %left and we are done.

https://github.com/php/php-src/blob/master/Zend/zend_language_parser.y#L73

--
Richard "Fleshgrinder" Fussenegger