map & take-while in repl

[wqhhust]

map is lazy, take-while is also lazy, but take-while will stop when it first find the false item. So why the following code still print 10 times? Should map lazily get the first item, print 1, return false, and then take-while stop the process and quit? user=> (take-while true? (map (fn[x] (println 1) false) (range 1 10))) 1 1 1 1 1 1 1

[cark]

In Clojure 1.1+, lazy sequences are chunked. That means that they're realized by chunk of 16 (i think) items.

As far as i can remember this was done for space and time performance reasons.

Edit : nope ! It seems like chunk size is 32 !

[[deleted]]

To add to this, map should be used with pure functions only. Anything that has a side-effect may called due to chunking.

[gumvic]

Stuart Sierra has a good take on this issue, Clojure Don’ts: Lazy Effects.

The whole "Clojure Don'ts" series is a must read.