On Sat, 25 Feb 2017 06:55:02 -0800, sml...@gmail.com wrote: > 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. > > ---------- > > 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 > > ---------- > This is Rakudo version 2017.02-95-g0be724727 built on MoarVM version > 2017.02-7-g3d859008 implementing Perl 6.c.

Thank you for the report. This is now fixed. Fix: https://github.com/rakudo/rakudo/commit/e8c6c259ce72fb5 Test: https://github.com/perl6/roast/commit/501f51b56c77fec06