在Clojure 1.2中:
(defprotocol PP
(foo [bar])
(foo [bar baz]))
=> PP
(extend-protocol PP
Object
(foo [bar] 1)
(foo [bar baz] 2))
=> nil
(foo "hello!")
=> #<CompilerException java.lang.IllegalArgumentException: No single method: foo of interface: PP found for function: foo of protocol: PP
我哪里做错了?我期望从foo函数的单参数版本中看到1作为结果,因为"hello!"显然是java.lang.Object的实例。