Waiting for I/O, and suggestions

[Jim Meehan <Meehan@YALE.ARPA>]

The description  of  the  various  READ  routines  says, "If no input is
available, then the end-of-file token is returned."   Depending  on  how
you interpret  "available,"  that's not true for (TERMINAL-INPUT); i.e.,
the T process will wait for input.

I don't know whether that feature is worth  generalizing;  i.e.,  should
you   be   able   to   define  your  own  input  stream  that  has  that
characteristic?  It might  be  handy  for  "mailboxes"  and  pipes,  for
instance.

Another addition,  probably  more  useful  but equally system-dependent,
is something along the lines of  (INPUT-AVAILABLE?   stream)  that  does
a conditional  read.   It's  hackable  now, but should it become part of
the standard language?
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