#4218: System.Random is way too lazy
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Reporter: EyalLotem | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.12.3
Keywords: random stack overflow | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Description changed by igloo:
Old description:
> randomRs is too lazy, generates lists of large lazy-state thunks, rather
> than lists of strict values.
>
> Test program is attached.
>
> Also, randomIO is too lazy, and builds up huge thunks. Using (randomIO
> >>= evaluate) is fine, however.
>
> Fails with stack overflow:
> rs <- replicateM 1000000 evaluate :: IO [Int]
> print $ last rs
>
> Works:
> rs <- replicateM 1000000 (evaluate =<< randomIO) :: IO [Int]
> print $ last rs
New description:
randomRs is too lazy, generates lists of large lazy-state thunks, rather
than lists of strict values.
Test program is attached.
Also, randomIO is too lazy, and builds up huge thunks. Using (randomIO >>=
evaluate) is fine, however.
Fails with stack overflow:
{{{
rs <- replicateM 1000000 evaluate :: IO [Int]
print $ last rs
}}}
Works:
{{{
rs <- replicateM 1000000 (evaluate =<< randomIO) :: IO [Int]
print $ last rs
}}}
--
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4218#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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