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•Use memoization in order to shortcut recursion for values that have already been calculated.

•Expose a sequence so that dependent values are cached before they are needed.

This approach is heap-consuming, in that it does cache all previously seen values. If this is a problem, you can in some situations eliminate it by selecting a more complex caching policy.

5.5 Wrapping Up

Clojure’s support for FP strikes a well-motivated balance between academic purity and effectiveness on the Java Virtual Machine. Clojure gives you access to a wide variety of techniques including self-recursion with recur, mutual recursion with trampoline, lazy sequences, and memoization.

Better still, for a wide variety of everyday programming tasks, you can use the sequence library, without ever having to define your own explicit recursions of lazy sequences. Functions like partition create clean, expressive solutions that are much easier to write.

If Clojure were an exclusively FP language, we would turn our attention next to the challenges of living in a world without mutable state and perhaps begin discussing the state monad. But Clojure leads us in a different direction with its most innovative feature: explicit APIs for managing mutable state. The Clojure concurrency API provides four different ways to model mutable state and is the subject of the next chapter.

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