From @raydiak

m​: my $a; BEGIN { $a := 1; say $a; }; say $a;
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤(Any)␤»

m​: my $a; BEGIN { $a = 1; say $a; }; say $a; # works with assignment
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤1␤»

From @AlexDaniel

Still reproducible (2017.11, HEAD(5929887)), but is supposed to work?

On 2015-02-09 17​:43​:52, raydiak@​cyberuniverses.com wrote​:

m​: my $a; BEGIN { $a := 1; say $a; }; say $a;
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤(Any)␤»

m​: my $a; BEGIN { $a = 1; say $a; }; say $a; # works with assignment
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤1␤»

The RT System itself - Status changed from 'new' to 'open'

From @zoffixznet

On Fri, 01 Dec 2017 12​:09​:05 -0800, alex.jakimenko@​gmail.com wrote​:

Still reproducible (2017.11, HEAD(5929887)), but is supposed to work?

Don't see any reason why that'd be questionable.

On 2015-02-09 17​:43​:52, raydiak@​cyberuniverses.com wrote​:

m​: my $a; BEGIN { $a := 1; say $a; }; say $a;
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤(Any)␤»

m​: my $a; BEGIN { $a = 1; say $a; }; say $a; # works with assignment
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤1␤»

Another manifestation of the same bug​:

<Zoffix__> m​: BEGIN { my $a1 := 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN { my $a1 = 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 = 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 := 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «(Mu)␤»

From @zoffixznet

On Tue, 30 Jan 2018 15​:08​:38 -0800, cpan@​zoffix.com wrote​:

On Fri, 01 Dec 2017 12​:09​:05 -0800, alex.jakimenko@​gmail.com wrote​:

Still reproducible (2017.11, HEAD(5929887)), but is supposed to work?

Don't see any reason why that'd be questionable.

On 2015-02-09 17​:43​:52, raydiak@​cyberuniverses.com wrote​:

m​: my $a; BEGIN { $a := 1; say $a; }; say $a;
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤(Any)␤»

m​: my $a; BEGIN { $a = 1; say $a; }; say $a; # works with assignment
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤1␤»

Another manifestation of the same bug​:

<Zoffix__> m​: BEGIN { my $a1 := 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN { my $a1 = 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 = 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 := 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «(Mu)␤»

Tracked this to Perl6​::World.compile_in_context but leaving it there, as it's getting too hard.
Need to gain a few levels first.

The comment in the method reads​:
  # Create outer lexical contexts with all symbols visible. Maybe
  # we can be a bit smarter here some day. But for now we just make a
  # single frame and copy all the visible things into it.

So I imagine the binding gets made to this faked out block and never propagates back to the source where all the lexicals were copied from.

From @zoffixznet

On Tue, 30 Jan 2018 19​:03​:13 -0800, cpan@​zoffix.com wrote​:

On Tue, 30 Jan 2018 15​:08​:38 -0800, cpan@​zoffix.com wrote​:

On Fri, 01 Dec 2017 12​:09​:05 -0800, alex.jakimenko@​gmail.com wrote​:

Still reproducible (2017.11, HEAD(5929887)), but is supposed to
work?

Don't see any reason why that'd be questionable.

On 2015-02-09 17​:43​:52, raydiak@​cyberuniverses.com wrote​:

m​: my $a; BEGIN { $a := 1; say $a; }; say $a;
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤(Any)␤»

m​: my $a; BEGIN { $a = 1; say $a; }; say $a; # works with
assignment
rakudo-{parrot,moar} 0cb22e​: OUTPUT«1␤1␤»

Another manifestation of the same bug​:

<Zoffix__> m​: BEGIN { my $a1 := 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN { my $a1 = 42; say $a1; }
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 = 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «42␤»
<Zoffix__> m​: BEGIN my $a1 := 42; say $a1;
<camelia> rakudo-moar deffe54b8​: OUTPUT​: «(Mu)␤»

Tracked this to Perl6​::World.compile_in_context but leaving it there,
as it's getting too hard.
Need to gain a few levels first.

The comment in the method reads​:
# Create outer lexical contexts with all symbols visible. Maybe
# we can be a bit smarter here some day. But for now we just make a
# single frame and copy all the visible things into it.

So I imagine the binding gets made to this faked out block and never
propagates back to the source where all the lexicals were copied from.

More comments​: https://irclog.perlgeek.de/perl6/2018-02-02#i_15769787

15​:11 jnthn Zoffix​: Yeah. Lexpads are immutable, and when we compile a BEGIN we obviously haven't finished the outer block yet, so we have to fake something up. But what? Containers are cloned from a "prototype", and the fake lexpad contains the static container. Thus what's actually happening is that on entry to the scope post-compilation, the Scalar is cloned complete with the value set in the prototype.
15​:12 Of course, binding doesn't have that level of indirection so there's no way it can work.
15​:12 We should perhaps detect it at compile time and say it can't work. Or...we could try diffing the scope after each BEGIN block and trying to somehow propagate bindings.