Multi-method non-redefine

gistfile1.clj

user=> (defmulti even-or-odd (fn [n] (if (even? n) :odd :even)))
#'user/even-or-odd
user=> (defmethod even-or-odd :even [n] "even")
#object[clojure.lang.MultiFn 0x7fd6a23b "clojure.lang.MultiFn@7fd6a23b"]
user=> (defmethod even-or-odd :odd [n] "odd")
#object[clojure.lang.MultiFn 0x7fd6a23b "clojure.lang.MultiFn@7fd6a23b"]
user=> (even-or-odd 1)
"even"
user=> ;; oops, let's try again

user=> (defmulti even-or-odd (fn [n] (if (even? n) :even :odd)))
nil
user=> (even-or-odd 1)
"even"

user=> ;; hmm. that didn't work

user=> (def even-or-odd nil)
#'user/even-or-odd
user=> (defmulti even-or-odd (fn [n] (if (even? n) :even :odd)))
#'user/even-or-odd
user=> (defmethod even-or-odd :even [n] "even")
#<MultiFn clojure.lang.MultiFn@1e9b11c>
user=> (defmethod even-or-odd :odd [n] "odd")
#<MultiFn clojure.lang.MultiFn@1e9b11c>
user=> (even-or-odd 1)
"odd"
user=> ;; finally