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  • Glasgow Haskell Compiler
  • GHCGHC
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  • #4218

Closed
Open
Opened Jul 24, 2010 by EyalLotem@trac-EyalLotem

System.Random is way too lazy

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
Edited Mar 09, 2019 by Ian Lynagh <igloo@earth.li>
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Reference: ghc/ghc#4218