Update: THIS IS A WRONG IMPLEMENTATION. PLease don't++ it!! Thanks, buk.

I'm getting different results from other people, so this is probably wrong, but then maybe not, so...

#! perl -slw
use strict;
use List::Util qw[ reduce ];

$a = $a; ## Disable the dumbest warning in perl!

my @samples = (
    ##    r1   r2   r3 
    [ qw[ 0.11 0.07 0.19 ] ],
    [ qw[ 0.43 0.31 0.37 ] ],
    [ qw[ 0.93 0.78 0.82 ] ],
    [ qw[ 0.91 0.12 0.15 ] ],
    [ qw[ 0.52 0.18 0.32 ] ],
);

sub P{ 
    return 1 if @_ == 1;
    my @r = @_;
    return reduce { 
         $a + ( $r[ $b ] - $r[ $b - 1 ] ) * P( @r[ 0 .. ( $#r - $b ) ]
+ ) 
    } 0 .. $#r;
}

my @results = map P( @$_ ), @samples;

print "@results";
__END__
P:\test>380259
0.1216 0.0744 0.0624999999999999 0.6541 0.2556
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