As often, Deparse comes to the rescue. With formatting adjusted for comparability with yours, the output is

#!/usr/bin/perl -w

my $true = "foo";
my $false = "0";
my $dc = "bar";

warn do { $dc if $false };
warn do { $dc unless $true };
warn do { $dc while $false };
warn do { $dc until $true };
warn do { if ($false) { $dc; } };
warn do { unless ($true) { $dc; } };
warn do { while ($false) { $dc; } };
warn do { until ($true) { $dc; } };
warn do { '0' };
warn do { 'foo' };
warn do { do { '0' } };
warn do { do { !1 } };
warn do { '0' };
warn do { !1 };
warn do { };
warn do { };

[download]

Note the !1 — ie "not true", ie "The Real False", which is an empty string in Perl5. That explains your something's wrong messages: the loops are getting folded away at compile time, but apparently the compiler doesn't evaluate hard enough.

Makeshifts last the longest.

In reply to Re^4: A cleaner way of scoping variables by Aristotle
in thread A cleaner way of scoping variables by bradcathey

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