Strange given/when deparsing

[KSURi]

Hello, monks!

There is a simple script:

use Modern::Perl;

my $x = 2.3;
given($x) {
    when(int) { say 'match' } # int($_) ~~ $x
    default { say 'no match' }
}

It prints 'no match' as expected.

There is also another script with a little difference:

use Modern::Perl;

my $x = 2.3;
given($x) {
    when($_) { say 'match' } # $_ ~~ $x
    default { say 'no match' }
}

Prints 'match' as expected.

The strangeness is that B::Deparse produces the same output for both scripts:

use Modern::Perl;
use warnings;
use strict 'refs';
BEGIN {
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
my $x = 2.3;
given ($x) {
    when ($_) {
        say 'match';
    }
    default {
        say 'no match';
    }
}

Why is this so? Is this a bug of B::Deparse?

[ikegami]

Is this a bug of B::Deparse?

Yes, although it *might* have already been fixed in forthcoming 5.10.1.

You can see the difference with the more precise (but verbose) B::Concise:

g                    <2> smartmatch sK*/2 ->h
d                       <0> padsv[$_:46,51] s ->e
f                       <1> int[t4] sK/1 ->g
e                          <0> padsv[$_:46,51] s ->f

f                    <2> smartmatch sK*/2 ->g
d                       <0> padsv[$_:46,51] s ->e
e                       <0> padsv[$_:46,51] s ->f

when(int) { say 'match' } # int($_) ~~ $x

You have the order backwards. It's $x ~~ int($_). (Well, $_ ~~ int($_) really.)

[akho]

Isn't ~~ commutative?

[ikegami]

It might have been. It might be. It won't be.

Update: Is the following clearer?

It might have been commutative in the past. It might be commutative now. It won't be commutative in the future.

[akho]

Very probably. Only perl can parse Perl, after all; and given/when is quite new.