ratom(X) or ratom(Stream,X)

The next lexical token on the current or specified input stream is bound to
X.  eg,

             : ratom(X)?
             > fred

             X = fred.

             : ratom(X)?
             > 123

             X = 123         % X is an integer

             : ratom(X)?
             > <=

             X = '<='

             : ratom(X)?
             > ,

             X = ','
