Except isn't that missing the actual point? The example was contrived to drive home that we can use objects as functions in ClojureScript - I respect that the e

Except isn't that missing the actual point? The example was contrived to drive home that we can use objects as functions in ClojureScript - I respect that the engaged reader understands that these tools must be applied tastefully. I could have implemented it just like you've shown but would we have learned anything? :) Also my example is one step from being open, extensible to any type instead of hard coding string/array which you copied. You can't do this in CoffeeScript in a safe way: (deftype Slice [start end] ISlice (-shift [_] (Slice. (inc start) (inc end))) IFn (-invoke [_ x] (-slice x start end)))