Hi,
for one of the problems from Project Euler I implemented a "triangle
numbers" lazy sequence after the blueprint of the fibonacci numbers
sequence in clojure.contrib.lazy-seqs:. When taking large numbers of
items from this equence, I get an out-of-memory exception:
user=> (def triangle-numbers
(let [rest-fn
(fn rest-fn [current cumulated]
(let [next (+ current cumulated)]
(lazy-cons next (rest-fn (inc current) next))))]
(rest-fn 1 0)))
#'user/triangle-numbers
user=> (nth triangle-numbers 1000000)
java.lang.OutOfMemoryError: Java heap space
java.lang.OutOfMemoryError: Java heap space
at java.math.BigInteger.add(BigInteger.java:1068)
at java.math.BigInteger.add(BigInteger.java:1041)
at clojure.lang.Numbers$BigIntegerOps.add(Numbers.java:793)
at clojure.lang.Numbers.add(Numbers.java:127)
at user.fn__2290$rest_fn__2292.invoke(Unknown Source)
at user.fn__2290$rest_fn__2292$fn__2294.invoke(Unknown Source)
at clojure.lang.LazyCons.rest(LazyCons.java:60)
at clojure.lang.RT.nth(RT.java:702)
at clojure.nth__440.invoke(boot.clj:830)
at user.eval__2303.invoke(Unknown Source)
at clojure.lang.Compiler.eval(Compiler.java:3891)
at clojure.lang.Repl.main(Repl.java:75)
If I understand it correctly this is the effect of the caching of the
lazy sequence. Is there a way to suppress the caching? Are there
alternatives in Clojure for representing and processing very large
sequences?
Thanks
Stephan
P.S.: I read the recent thread "memory issue with nth", but it is not
clear to me whether this is the same problem.
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