CODEWITHSUNDEEP
clojure
David
David

Reputation: 3056

Why is reduce not causing a stackoverflow in clojure?

Suppose you have this code:

(reduce + 1 (range 1 13000))

Should this not cause a stackoverflow, because it is not tail call optimized? Or is reduce similar to loop?

Upvotes: 0

Views: 125

Answers (1)

Alex Miller
Alex Miller

Reputation: 70239

A reduce will effectively be a loop over the values of the collection.

I say "effectively" because there are actually many different reduce implementation strategies employed by Clojure, depending on the type of the collection. This includes seq traversal via first/next, reduction via iterator, and collections that know how to self-reduce more efficiently.

In this case, the call to range actually returns a LongRange object which implements the IReduceInit interface for self reduction and actually does a tight do/while loop (implemented in Java).

The code for this can be found here in the latest release.

Upvotes: 6

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