[Haskell-cafe] Space leak with replicateM

Ken Takusagawa II ken.takusagawa.2 at gmail.com
Tue Jun 16 07:37:58 UTC 2015

In the following program, the function "test1" results in huge memory
usage, but substituting "test2", which does essentially the same thing,
does not.  GHC 7.10.1, AMD64.  Is there a different implementation of
replicateM that avoids the space leak?

module Main where {
import Control.Monad;

numbers :: [Int];

-- has a space leak
test1 :: [[Int]];
test1 = replicateM 4 numbers;

-- no space leak
test2 :: [[Int]];
test2 = do {
x1 <- numbers;
x2 <- numbers;
x3 <- numbers;
x4 <- numbers;
return [x1,x2,x3,x4];

main :: IO();
main = print $ length $ test1;


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