The full featured life of the interpreter begins after
boot-strapping with sli-init.sli by pushing the start symbol.
When no commandline arguments are present the start symbol
prepares for an interactive session in the shell with the
help of the executive command. When command line arguments
are present a non-interactive session is assumed and the start
symbol prepares for recognition of these
arguments with the help of the :commandline command.
When executing files and an error is raised that is not
caught by the script quit with the exit code scripterror which
is defined in the exitcodes dictionary in statusdict.
start does not take any arguments. It evaluates the length
of argv which resides in the statusdict.