load [exp];
This loads a NESL file into the current environment. If present,
the expression exp must evaluate to a string (sequence of
characters) and be a valid filename. If the filename ends with the
suffix ``.nesl'', the suffix can be omitted. If exp is
omitted, it defaults to the last file that was loaded, or edited using
edit (see Section 4.2). Files are loaded
relative to the current directory. NESL files can contain any
NESL top-level expressions or top-level commands; a file can
therefore load other files, or set various environment variables, such
as the memory size (see Section 3.5).