# New Ticket Created by Sam S.
# Please include the string: [perl #130859]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=130859 >
A WhateverCode containing an array subscript that is itself a
WhateverCode, usually works fine... e.g. `*.[*-1]` always returns the
last positional element of its argument.
A WhateverCode closing over a lexical variable usually works fine,
e.g. `* - $x` always subtracts the *current* value of $x from its
argument.
But when *both* of those features are combined, *and* the variable
that is closed over is scoped to an outer block or routine that is
called repeatedly, then it misbehaves:
sub f { my $x = ++$; (*.[* - $x])(<a b c>) }
say (f,f,f); # (c c c)
The same, using `map`:
say (1..3).map: { (*.[* - $_])(<a b c>) }; # (c c c)
The expected output would be `(c b a)`. For some reason, it seems to
use the first value of `$x` or `$_` for all three iterations.
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Demonstration that the particular circumstances described above have
to align for the bug to appear:
1) If the WhateverCode subscript is replaced with a static expression,
the bug disappears:
say (1..3).map: { (*.[3 - $_])(<a b c>) }; # (c b a)
2) If the outer WhateverCode is removed by "inlining" it, the bug disappears:
say (1..3).map: { <a b c>[* - $_] }; # (c b a)
3) If the `map` is unrolled so that there is no outer block that gets
re-entered between invocations of the WhateverCode's, the bug
disappears:
my &f = *.[* - $_];
$_ = 1; say f <a b c>; # c
$_ = 2; say f <a b c>; # b
$_ = 3; say f <a b c>; # a
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This is Rakudo version 2017.02-95-g0be724727 built on MoarVM version
2017.02-7-g3d859008 implementing Perl 6.c.
