Tail recursion would be a great optimization to have, but Perl doesn't do it except through the clunky use of goto BLOCK;. And that doesn't appear to give any time optimization (admittedly, that p5p message could be long out of date).

I think you mean goto ⊂ 

#!perl 
use strict;
use Benchmark;

sub normal {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    return normal(@_);
}

sub tail {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    goto &tail;
}

timethese( 10, {
        "normal" => sub { normal(500000) },
        "tail"   => sub {   tail(500000) },
    }
);

[download]
Output: 
    normal: 25 wallclock secs (23.19 usr +  0.59 sys = 23.78 CPU) @  0
+.42/s (n=10)
      tail: 18 wallclock secs (17.44 usr +  0.03 sys = 17.47 CPU) @  0
+.57/s (n=10

[download]
Not very impressive, but there is a clear improvement in speed. The improvement in wallclock seconds becomes far larger if you start swapping with the normal recursive call (at my machine at 1_000_000 levels of recursion). I tried this only with 1 iteration because I got impatient: 
#!perl 
use strict;
use Benchmark;

sub normal {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    return normal(@_);
}

sub tail {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    goto &tail;
}

timethese( 1, {
        "normal" => sub { normal(1000000) },
        "tail"   => sub {   tail(1000000) },
    }
);

[download]
output: 
Benchmark: timing 1 iterations of normal, tail...
    normal: 123 wallclock secs ( 6.58 usr +  1.13 sys =  7.71 CPU) @  
+0.13/s (n=1)
            (warning: too few iterations for a reliable count)
      tail:  3 wallclock secs ( 3.50 usr +  0.01 sys =  3.51 CPU) @  0
+.28/s (n=1)
            (warning: too few iterations for a reliable count)

[download]
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Tail recursion using goto ⊂ (was: Re^3: Trinary Operator Semantics) by Joost
in thread Trinary Operator Semantics by hardburn

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