Getting Clojure

Staying Out of Trouble

While lazy—and particularly unbounded— sequences are a powerful programming tool, dealing with them in the REPL has its issues. You certainly don’t want to try to print an entire infinite sequence, either explicitly, like this:

user=> (def numbers (iterate inc 1))
#'user/numbers

user=> (println numbers)   ; Say goodnight!

or implicitly:

user=> numbers             ; And that is it!

Never try to stare into the face of the infinite. This is where the *print-length* dynamic var and set!, both of which we saw back in Chapter 8, ​Def, Symbols, and Vars​, come in handy:

user=> (set! *print-length* 10)
10

user=> numbers
(1 2 3 4 5 6 7 8 9 10 ...)

More subtly, you also need to be careful about side effects when ...