(define (make-port-mapping)
(make-hash-table))
-(define (port-mapping-set! port-mapping port #:optional read write except)
+(define* (port-mapping-set! port-mapping port #:optional read write except)
"Sets port-mapping for reader / writer / exception handlers"
(if (not (or read write except))
(throw 'no-handlers-given "No handlers given for port" port))