This is the nucleus of a PostScript interpreter.  There's a dreadful
hack in Interp.nw to support operators that raise exceptions not
listed there (the ``error exceptions'').  Because of that hack, I need
to include the Error interface here in order to be able to instantiate
the interpreter for use by the debugger.  Gross, Gross.

You can build a standalone interpreter without any debugging goo by
making `smallinterp'.

The *.ops files are used to add operators to the interpreter.  That
stuff runs through psgen.icn to produce Modula-3 code.  psgen is a
horror and an abomination, and the specification language it
implements is completely undocumented.  Maybe one day I'll be inspired
to do a better job, but you may still get some use out of it.
