On 03/18/2013 02:14 PM, Gregory Collins wrote:
Put a bang pattern on your accumulator in "go". Since the value is not
demanded until the end of the program, you're actually just building up
a huge space leak there.
Fixed that
Secondly, unconsing from the lazy bytestring will cause a lot of
allocation churn in the garbage collector -- each byte read in the input
forces the creation of a new "L.ByteString", which is many times larger.
Nope. L.ByteString is created along with strict ByteString but content
not copied. And, in fact, that not a problem. The problem is that GHC
unable to optimize constantly changing state in State monad. I don't
know is it posible or not and if it is than what should I do to allow
such optimization.
import Control.Monad.State.Strict
data S6 = S6 Int Int
main_6 = do
let r = evalState go (S6 10000 0)
print r
where
go = do
(S6 i a) <- get
if (i == 0) then return a else put (S6 (i - 1) (a + i)) >> go
main_7 = do
let r = go (S6 10000 0)
print r
where
go (S6 i a)
| i == 0 = a
| otherwise = go $ S6 (i - 1) (a + i)
main = main_7
If I run main_6 I get constant allocations. If I run main_7 I get no
allocations.
Does anybody know how to overcome this inefficiency?
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