read(X) or read(Stream, X)

The  next term, delimited by a "fullstop" (ie.  a '.' followed by <cr> or a
space),  is read from the current or given input stream and unified with X.
The  syntax of the term must accord with current operator declarations.  If
a  call  'read(X)' causes the end of the stream to be reached, X is unified
with the term "end_of_file".  If input comes from the terminal, the user is
prompted by "> ".
