[plt-scheme] no #!eof

On Apr 15, Abdulaziz Ghuloum wrote:
> 
> On Apr 15, 2008, at 1:06 AM, Eli Barzilay wrote:
> 
> > What about:
> >
> >> (read)
> >   (
> >   1
> >   ^D
> >   2
> >   )
> >
> > At least in the old version of Chez I get
> >
> >   Error in read: unexpected end-of-file.
> >
> > right after the ^D, but I get (1 #!eof 2) if I use `#!eof' instead of
> > ^D.
> 
> Right.  This is because, as Matthew said, "a reader can treat an eof
> in the character stream as different from a representation of a
> literal eof."

(Right.)


> Read returns an eof if the first thing it sees is a ^D, but signals
> an error if it sees a ^D while trying to parse a datum (e.g., if you
> try to read from the string "(", you get an error since there is a
> "character stream" eof after the left parenthesis).  Read doesn't
> signal an error for the eof objects it constructs itself since there
> is no "character stream" eof in #!eof.

(And that difference between #!eof and a "character stream eof" is the
part that is asking for trouble...)

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!