Clojure High Performance Programming - Second Edition

Parallelism with reducers

Reducers are a new abstraction introduced in Clojure 1.5, and are likely to have a wider impact on the rest of the Clojure implementation in the future versions. They depict a different way of thinking about processing collections in Clojure—the key concept is to break down the notion that collections can be processed only sequentially, lazily, or producing a seq, and more. Moving away from such a behavior guarantee raises the potential for eager and parallel operations on one hand, whereas incurring constraints on the other. Reducers are compatible with the existing collections.

For an example, a keen observation of the regular map function reveals that its classic definition is tied to the mechanism (recursion), order ...