From @masak

<TimToady> nr​: sub r2cf(Rat $x is copy) { gather $x [R/]= 1 while ($x
-= take $x.floor) > 0 }; say r2cf(1.4142136)
<p6eval> rakudo 935c90​: OUTPUT«===SORRY!===␤Preceding context expects
a term, but found infix = instead␤at /tmp/WXbDH1h_R_​:1␤------> b
r2cf(Rat $x is copy) { gather $x [R/]=⏏ 1 while ($x -= take $x.floor)

0 }; sa␤»
<p6eval> ..niecza v24-18-gaf64300​: OUTPUT«1 2 2 2 2 2 2 2 2 2 6 1 2 4 1 1 2␤»
<TimToady> dunno if you have that one yet
<masak> don't think so.
* masak submits TimToady's rakudobug
<masak> r​: my $x; $x [R/]= 1
<p6eval> rakudo 935c90​: OUTPUT«===SORRY!===␤Preceding context expects
a term, but found infix = instead␤at /tmp/95XYnmRMtC​:1␤------> my $x;
$x [R/]=⏏ 1␤»

From @usev6

This works now with Rakudo​:

$ perl6 -e 'my $x = 5; $x [R/]= 1; say $x'
0.2

$ perl6 -e 'sub r2cf(Rat $x is copy) { gather $x [R/]= 1 while ($x -= take $x.floor) > 0 }; say r2cf(1.4142136)'
1 2 2 2 2 2 2 2 2 2 6 1 2 4 1 1 2

I added a test to S03-metaops/reverse.t with commit Raku/roast@4dca70c8ee

I'm closing this ticket now.

@usev6 - Status changed from 'new' to 'resolved'