Re^4: A cleaner way of scoping variables

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 { };
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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.

Comment on Re^4: A cleaner way of scoping variables Download Code

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Re^5: A cleaner way of scoping variables by ikegami (Patriarch) on Oct 21, 2005 at 15:09 UTC
Nit: "The Real False" is not the empty string. It's the empty string in string context and 0 in numerical context. You can see the differnce using the following snippet: `use warnings; print(("")+1, "\n"); print((!1)+1, "\n");` [download] If "The Real False" was simply an empty string, we'd see two warnings instead of `Argument "" isn't numeric in addition (+) at script.pl line 2. 1 1` [download]	[reply] [d/l] [select]

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Re^5: A cleaner way of scoping variables
by ikegami (Patriarch) on Oct 21, 2005 at 15:09 UTC

Nit: "The Real False" is not the empty string. It's the empty string in string context and 0 in numerical context. You can see the differnce using the following snippet:

use warnings;
print(("")+1, "\n");
print((!1)+1, "\n");
[download]

If "The Real False" was simply an empty string, we'd see two warnings instead of

Argument "" isn't numeric in addition (+) at script.pl line 2.
1
1
[download]

[reply]
[d/l]
[select]