Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!comp.vuw.ac.nz!cc-server4.massey.ac.nz!massey!E.Ireland
From: E.Ireland@@massey.ac.nz (Evan Ireland)
Newsgroups: comp.lang.scheme
Subject: Re: evaluating () should be an error
Message-ID: <514sis-d@@massey.ac.nz>
Date: 24 Mar 91 21:10:49 GMT
References: <1991Mar24.064144.4256@daffy.cs.wisc.edu>
Reply-To: E.Ireland@@massey.ac.nz
Organization: Information Sciences, Massey University, New Zealand
Lines: 16


>Are there any scheme implementations that signal an error on evaluating () ?

I wrote a Scheme interpreter in Tui (a now non-existent functional
language) a couple of years ago, and I did trap this condition, but
perhaps in an interesting way: instead of a read-eval-print loop, I
had a read-rewrite-eval-print loop.  The rewrite step involved
recognition of special forms and macro expansion.

Null procedure calls (unquoted ()) were recognised during rewriting,
rather than during evaluation.  Thus you could never encounter an
unquoted () during evaluation (unless your program called load).
_______________________________________________________________________________

E.Ireland@massey.ac.nz          Evan Ireland, School of Information Sciences,
  +64 63 69099 x8541          Massey University, Palmerston North, New Zealand.