ClojureScript: Up and Running

Chapter 6. Sequences

One of the key features of the Lisp family of languages is their orientation around lists—not just as data structures, but as a structural metaphor for algorithms and execution flow. Recursive algorithms, for example, can be very cleanly structured around lists in Lisp variants.

Unfortunately, in most Lisps, this metaphor is tightly bound to the actual implementation of a singly-linked list, which has performance characteristics that make it unsuitable for many purposes.

To resolve this problem, Clojure introduced a new abstraction around the concept of a list, called a sequence, which is shared by ClojureScript. A sequence is a logical list, similar to those in most Lisps, with a well-defined set of operations. However, Clojure sequences are not a concrete type, but rather an abstract contract that may be satisfied concretely by a variety of different types of objects. All of ClojureScript’s collections, as well as many other types of logical collections in JavaScript, can be used as sequences. This allows ClojureScript code to be constructed in an idiomatic list-based Lisp style, while using whatever data structure is actually most appropriate for the job.

Many common operations in ClojureScript are part of the sequence API. Functions from the sequence API are used to select items from sequences, add items to sequences, and produce, consume, and transform sequences. Understanding how sequences work will give you a major leg up in understanding and writing idiomatic ...