Hey, I'm trying to Perl some BIO past papers (a British programming contest) but I have some results that I can't explain. The program has to take in a string where b, i and o are functions and have coefficients and groupings such as b3(io) does b then io 3 times. Full explanation is here (question two):

BIO Past Papers

Ok, I finally checked the full explanation. Here's my sample code to solve the assignment:

#!/usr/bin/perl -l

use strict;
use warnings;

my @pack=1..8;

my %disp;
@disp{qw/b i o/}=map {
    my $t=$_;
    sub { @_[@$t] };
} [1..7,0],
  [4,0,5,1,6,2,7,3],
  [0,4,1,5,2,6,3,7];

sub parse {
    for (@_) {
        my $c;
        s/[()]/
          $& eq '(' ?
          '(=' . $c++ . '=' :
          '=' . --$c . '=)' /ge;
        s/(\d)([bio])/$2 x $1/ge;

        1 while s/(\d)
                  \(=(\d+)=
                  (.+?)
                  =\2=\)/$3 x $1/gex;
    }
}

while (<>) {
    parse $_;
    @pack=$disp{$_}->(@pack) for /./g;
    print "@pack";
}

__END__
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Please note that:

1. I don't do any input validation, for the rules partly explicitly partly implicitly state that I must trust it,
2. this is certainly not the most efficient way to do this, but it is IMHO adequate to the nature of the problem, as of the description,
3. Also, the sub parse() is by no means necessary, but I wanted to keep it separate it from the main loop.

   HTH.

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