Exceptions and debugging 

# In .../Canvas.pm

my $radius = $opt{radius}
    or confess "draw_circle needs radius";

• stack trace

draw_circle needs radius at /path/to/Canvas.pm line 18.
    Canvas::draw_circle('Canvas=HASH(0x17e7998)', 'x', 100, 'y', 250, 'color',
        '#ff0000') called at ./map-branches.pl line 847
    main::add_one_store('x', 304, 'y', 228, 'name', 'Albany') called at
        ./map-branches.pl line 622
    main::overlay_stores() called at ./map-branches.pl line 318
    main::render_map() called at ./map-branches.pl line 245
    main::add_map_image('PDF::Builder::Page=HASH(0x83177c7)') called at
        ./map-branches.pl line 108
    main::generate_pdf('./branches.pdf') called at ./map-branches.pl line 42