Couldn't the compiler infer that the 2 expressions are identical with
identical arguments and perform the reduce only once? Basically what the
programmer would do in a let statement? Would that be too expensive?
Jim
On 05/02/13 15:21, Herwig Hochleitner wrote:
Clojure has a feature called locals clearing, which sets 'coll to nil
before calling reduce in test1, because the compiler can prove it
won't be used afterwards.
In test2, coll has to be retained, because reduce is called a second
time on it.
2013/2/5 N8Dawgrr <nathan.r.matth...@gmail.com
<mailto:nathan.r.matth...@gmail.com>>
If the head is retained on a lazy sequence we have a potential
memory leak.
I set my JVM memory low, 64mb and ran the following:
user> (defn test1 [coll] (reduce + coll))
#'user/test1
user> (test1 (take 10000000 (iterate inc 0)))
49999995000000
user>
Now if we do:
user> (defn test2 [coll] [(reduce + coll) (reduce + coll)])
#'user/test2
user> (test2 (take 10000000 (iterate inc 0)))
OutOfMemoryError Java heap space [trace missing]
user>
Which OOMs as expected. The question is, why doens't the first
example blow up? What magics happening?
I would expect coll which is a function argument to be retained by
the garbage collector and hence blow up.
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