Making a list "unlazy" in clojure

Question

I recently noticed that there was a very clear implementation of insertion sort here :

Insertion sort in clojure throws StackOverFlow error

which suffers from a memory overflow, due to the fact that concat lazily joins lists. I was wondering :

What strategies can we apply to "de-lazying" a list when we want better performance on large collections ?

Hmm... After some more googling, its clear that the simple answer to this question is by using the "doall" function to wrap the collection. However, I assume there might be some gotchas here which might be useful to know about. — jayunit100
– jayunit100, Commented Mar 26, 2012 at 0:18

mikera · Accepted Answer · 2012-03-26 03:32:00Z

6

doall is certainly fine for forcing lazy evaluation.

Another useful thing to remember is that reduce is non-lazy. This can therefore be very useful in large computations for ensuring that intermediate results get evaluated and reduced to a single output value before the computation proceeds.

answered Mar 26, 2012 at 3:32

mikera

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2 Comments

kotarak Over a year ago

I don't quite understand the downvote. doall will do the job and a reduce accumulating into a vector also provides a solution, which shouldn't be dismissed immediatelly. The result has fast random access which might be interesting for certain applications. (That said: a vec around the resulting sequence would also give the same result.)

jayunit100 Over a year ago

I agree do all would work... In fact, it did work I tried it just after posting this question, regarding the other referenced post. Please comment.

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