Question

I frequently find myself wanting to efficiently run a Clojure function multiple times with an integer index (like “dotimes”) but also get the results out as a ready-made sequence/list (like “for”).

i.e. I’d like to do something like this:

(fortimes [i 10] (* i i))

=> (0 1 4 9 16 25 36 49 64 81)

Clearly it would be possible to do:

(for [i (range 10)] (* i i))

But I’d like to avoid creating and throwing away the temporary range list if at all possible.

What’s the best way to achieve this in Clojure?

Answer 1

I’ve written an iteration macro that can do this and other types of iteration very efficiently. The package is called clj-iterate, both on github and clojars. For example:

user> (iter {for i from 0 to 10} {collect (* i i)})
(0 1 4 9 16 25 36 49 64 81 100)

This will not create a temporary list.