Input / Output


KEY
     2.1.1  Reading in Programs
     2.1.2  File Handling
     2.1.3  Input and Output of Terms
     2.1.4  Character Input/Output


A  total  of  ten I/O streams may be open at any one time for input and output.
This includes a stream that is always available for input  and  output  to  the
user's  terminal.  A stream to a file F is opened for input by the first see(F)
executed.  F then becomes the current input stream.   Similarly,  a  stream  to
file  H is opened for output by the first tell(H) executed.  H then becomes the
current output stream.  Subsequent calls to see(F) or to tell(H) make  F  or  H
the  current  input  or  output  stream,  respectively.  Any input or output is
always to the current stream.

When no input or output stream has been specified,  the  standard  ersatz  file
'user',  denoting the user's terminal, is utilised for both.  When the terminal
is waiting for input on a new line, a prompt will be displayed as follows:

            "|    "   -  top-level continuation line.
            "| "      -  during consult(user).
            "|: "     -  default for read from user program.

When the current input (or  output)  stream  is  closed,  the  user's  terminal
becomes the current input (or output) stream.

No  file except the ersatz file 'user' can be simultaneously open for input and
output.

A file is referred to by its name, written as an atom, e.g.

            myfile
            'F123'
            'DATA#LST'
            'ecmi25.greeks'

All I/O errors normally cause an abort, except for the effect of the  evaluable
predicate nofileerrors decribed below.
End of file is signalled on the user's terminal by issuing a ^Y (Control and Y)
character.    Any  more  input  requests  for a file whose end has been reached
causes an error failure.