How do I make the alter function/ assoc function return nil?

Question

I have a really really huge hash table and whenever I try to alter the hash, the entire hash is returned, which crashes my REPL. Is there a way I can ask Clojure to just set the value and return nil?

Thank You.

Answer 1

No. Clojures data types are immutable. Also they use shared structure so actually creating a new value is very very cheap for memory and performance. There are options to increase the memory available to the JVM like java -server. Also you can create Java objects which are mutable if you really need them.

Answer 2

dorun always returns nil:

(dorun (alter ...))

If all you want is to prevent the REPL from printing huge data structures, use *print-level* or *print-length*.

user> (set! *print-level* 2)
2
user> {:foo {:bar {:baz {:quux 1}}}}
{:foo {:bar #}}
user> (set! *print-length* 2)
2
user> (range 100)
(0 1 ...)