Yes, the implementation of instance Random Int in GHC's library pre-dates the existence of the genRange class operation for RandomGen. GHC's implementation of the instance behaves extremely badly when given a random generator with only two values (as in your example). I would love someone to send me a better implementation of the Random library. Preferably someone who understands the pitfalls. Simon | -----Original Message----- | From: Ian Lynagh [mailto:igloo@earth.li] | Sent: 29 November 2001 15:32 | To: haskell@haskell.org | Subject: Confused about Random | | | | With the following module: | | module Main where | | import Random | | data Foo = Foo StdGen | | main :: IO() | main = do let rs = randoms (Foo (mkStdGen 39)) :: [Int] | rRs = randomRs (0,9) (Foo (mkStdGen 39)) :: [Int] | putStrLn $ show $ take 100 rs | putStrLn $ show $ take 100 rRs | | instance RandomGen Foo where | genRange _ = (0, 1) | next (Foo g) = (val `mod` 2, Foo g') | where (val, g') = random g | split _ = error "Not implemented" | | ghc gives me | | [-2147476078,7482,-2147476078,-2147476078,-2147476079,-2147476 | 078,7483,7482,7482,-2147476079,-2147476078,-2147476079,-214747 | 6079,7482,-2147476078,-2147476078,-2147476078,-2147476079,7482 | ,7483,7482,7483,7482,-2147476078,-2147476078,-2147476078,7483, | -2147476079,7482,-2147476078,-2147476079,-2147476078,7483,-214 | 7476079,7483,7482,-2147476079,7483,7482,7483,-2147476078,-2147 | 476079,-2147476079,7482,-2147476078,7482,-2147476079,-21474760 | 79,7482,-2147476078,7483,7483,-2147476079,-2147476078,7483,748 | 3,-2147476078,-2147476079,-2147476078,-2147476079,-2147476078, | 7483,7483,7482,7482,7483,-2147476078,-2147476079,-2147476079,7 | 482,7483,-2147476078,-2147476079,-2147476079,-2147476078,7482, | 7483,-2147476079,7482,7482,7482,7483,-2147476079,-2147476079,- | 2147476078,7482,7482,7482,7482,-2147476079,7482,7482,-21474760 | 79,7483,-2147476078,7482,7483,-2147476079,-2147476079,7482] | [1,2,2,1,1,2,1,2,1,1,1,2,2,2,2,1,2,1,1,1,1,2,1,1,1,1,2,1,1,2,1 | ,2,1,2,1,1,2,1,2,2,2,1,2,2,2,1,1,2,1,2,1,2,2,2,1,1,2,1,1,2,1,1 | ,1,2,2,2,1,1,2,2,2,1,1,1,2,2,2,1,2,2,1,2,1,1,1,1,2,1,1,2,2,1,1 | ,1,1,1,2,1,1,2] | | The first list doesn't seem to cover the whole spectrum and I | was expecting the second list to be composed over 0s through | 9s. Is my understanding wrong? | | nhc complains | Context for Random.Random needed in left hand pattern at | 17:11. and hugs doesn't seem to know genRange exists. With it | commented out it returns the same as ghc. | | | Thanks | Ian | | | _______________________________________________ | Haskell mailing list | Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell |