:- use_module(library(optparse)).(can be autoloaded)
Opts is a list of parsed options in the form Key(Value).
Dashed args not in OptsSpec are not permitted and will raise
error (see tip on how to pass unknown flags in the module description).
PositionalArgs are the remaining non-dashed args after each
flag has taken its argument (filling in
for booleans). There are no restrictions on non-dashed arguments and
they may go anywhere (although it is good practice to put them last).
Any leading arguments for the runtime (up to and including '--') are