my $munger=Munger->new( input => "data" );

# assume the original "data"
# since there's no Foo::IO argument
my $sort_result = $munger->sort(by => "date"); 

# Again, just use the input filename stored in 
# the main object - "data"
my $mangle_result = $munger->mangle(); 

# Use sorted file, and know that it's sorted by date
# Give it the sort result Foo::IO state object
my $subset_result = $munger->subset( by => date,
                                     $sort_result
                                    ); 
# etc.