(next [4 5 6] ) # => 0 (next [4 5 6] 0 ) # => 1 (next [4 5 6] 1 ) # => 2 (next [4 5 6] 2 ) # => nil # note that dictionary keys are not necessarily in the same order # as the corresponding literal. (next {:a 5 :b 6 :c 7} ) # => :a (next {:a 5 :b 6 :c 7} :a ) # => :c (next {:a 5 :b 6 :c 7} :c ) # => :b (next {:a 5 :b 6 :c 7} :b ) # => nil