( -- flag
Attempt to fill the input buffer from the input source,
returning a true flag if successful.
When the input source is the user input device, attempt to
receive input into the terminal input buffer. If successful,
make the result the input buffer, set >IN
to zero, and
. Receipt of a line containing no characters
is considered successful. If there is no input available from
the current input source, return false
When the input source is a string from EVALUATE
and perform no other action.
REFILL is designed to behave reasonably for all possible
input sources. If the input source is coming from the user,
REFILL could still return a false value if, for instance,
a communication channel closes so that the system knows that no
more input will be available.