#!/usr/bin/perl                                                                                                                                                                                             
use Data::Dumper;

my $clauses;

push(@$clauses, ["==","a","b"]);
push(@$clauses, "and");
push(@$clauses, ["==","c","d"]);
push(@$clauses, "or");
push(@$clauses, ["==","e","f"]);
push(@$clauses, "and");
push(@$clauses, ["==","g","h"]);

$Data::Dumper::Indent = 0;                                                                                                                                                                                 

my $list = BuildList($clauses);
print Dumper($list). "\n";


sub BuildList($)
{
    my $clauses = shift();
    my $list;

    while(my $clause = shift(@$clauses))
    {
        if($clause eq "and")
        {
            $list = ['AND',[$list], [shift(@$clauses)]];
        }
        elsif($clause eq "or")
        {
            $list = ["OR",[$list, BuildList($clauses)]];
        }
        else
        {
            $list = $clause
        }
    }
    return($list);
}

##</code><code>##

['OR',[['AND',[['==','a','b']],[['==','c','d']]],['AND',[['==','e','f']],[['==','g','h']]]]]