R4RS 6.10.3  (write-char char)              ==>  unspecific
             (write-char char output-port)  ==>  unspecific

Writes the character CHAR (not an external representation of the
character) to the given port and returns an unspecified value. The
OUTPUT-PORT argument may be omitted, in which case it defaults to
the value returned by CURRENT-OUTPUT-PORT.
