[Haskell-cafe] Space leak with replicateM

[Joachim Breitner]

Hi,

Am Dienstag, den 16.06.2015, 03:37 -0400 schrieb Ken Takusagawa II:
> 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];
> numbers=[1..200];
> 
> -- 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;
> 
> }
> 

Could be the state hack causing `numbers` to inline, see
http://stackoverflow.com/questions/29404065/why-does-this-haskell-code-run-slower-with-o/30603291#30603291
and
https://ghc.haskell.org/trac/ghc/ticket/9349

Greetings,
Joachim

-- 
Joachim “nomeata” Breitner
  mail at joachim-breitner.de • http://www.joachim-breitner.de/
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  Debian Developer: nomeata at debian.org
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