package Foo;

use strict;
use warnings;
use Carp;

my %subs = (
    subA => _gen_tr('abc' => 'xyz'),
    subB => _gen_tr('ijk' => 'qrs'),
);

$subs{reverse($_)} = $subs{$_} for keys %subs; # Stand-in example for aliases
no strict 'refs';
*$_ = $subs{$_} for keys %subs;

require Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = keys %subs;

sub _gen_tr {
    /^\w+$/ or confess "Non-word characters in argument: <$_>" for @_;
    eval "sub { shift =~ tr/$_[0]/$_[1]/r }" 
}

1;