So... I must say I am rather pleased with the following code.
It allows you to use any value of type Bounded and Enum as a member of
Random, or Arbitrary, which means you can quickCheck properties on it
as well.
For quickchecking, the code below "cheats" by not defining the
coarbitrary funciton, which I confess I don't really understand and
never use.
Even so, I can see myself using this in a number of places... Does it
seem reasonable to add a ticket to get this added to
http://hackage.haskell.org/packages/archive/QuickCheck/2.1.0.1/doc/html/Test...
perhaps modulo the definition of an appropriate coarbitrary function?
thomas.
thartman@patchwiki:~/haskell-learning/testing>cat BoundedEnum.hs
{-# LANGUAGE FlexibleInstances, UndecidableInstances,
ScopedTypeVariables, OverlappingInstances #-}
module Main where
import Test.QuickCheck
import System.Random
class (Bounded a, Enum a) => BoundedEnum a
instance (Bounded a, Enum a) => BoundedEnum a
instance BoundedEnum a => Random a
where random g =
let min = fromEnum (minBound :: a)
max = fromEnum (maxBound :: a)
(i,g') = randomR (min,max) $ g
in (toEnum i,g')
randomR (low,high) g =
let min = fromEnum low
max = fromEnum high
(i,g') = randomR (min,max) $ g
in (toEnum i,g')
instance BoundedEnum a => Arbitrary a
where arbitrary = do
let min = fromEnum (minBound :: a)
max = fromEnum (maxBound :: a)
i <- arbitrary
return . toEnum $ min + (i `mod` (max-min))
coarbitrary = undefined
data DayOfWeek
= Monday
| Tuesday
| Wednesday
| Thursday
| Friday
| Saturday
| Sunday
deriving (Show, Read, Eq, Enum, Ord, Bounded)
t :: IO DayOfWeek
t = randomIO
t2 :: IO Int
t2 = randomIO
pDayEqualsItself :: DayOfWeek -> Bool
pDayEqualsItself day = day == day -- a trivial property, just so we can show
t3 = quickCheck pDayEqualsItself
-- show what days are being tested
t4 = verboseCheck pDayEqualsItself
2009/5/1 michael rice
I'm using the code below to generate random days of the week [Monday..Sunday].
Is there a better/shorter way to do this?
Michael
==============
[michael@localhost ~]$ ghci dow GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( dow.hs, interpreted ) Ok, modules loaded: Main. *Main> random (mkStdGen 100) :: (DayOfWeek, StdGen) Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. (Friday,4041414 40692) *Main> random (mkStdGen 123) :: (DayOfWeek, StdGen) (Tuesday,4961736 40692) *Main>
==============
import System.Random
data DayOfWeek = Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday deriving (Show, Read, Eq, Enum, Ord, Bounded)
instance Random DayOfWeek where randomR (a,b) g = case (randomIvalInteger (toInteger (dow2Int a), toInteger (dow2Int b)) g) of (x, g) -> (int2Dow x, g) where dow2Int Monday = 0 dow2Int Tuesday = 1 dow2Int Wednesday = 2 dow2Int Thursday = 3 dow2Int Friday = 4 dow2Int Saturday = 5 dow2Int Sunday = 6
int2Dow 0 = Monday int2Dow 1 = Tuesday int2Dow 2 = Wednesday int2Dow 3 = Thursday int2Dow 4 = Friday int2Dow 5 = Saturday int2Dow 6 = Sunday
random g = randomR (minBound,maxBound) g
randomIvalInteger :: (RandomGen g, Num a) => (Integer, Integer) -> g -> (a, g) randomIvalInteger (l,h) rng | l > h = randomIvalInteger (h,l) rng | otherwise = case (f n 1 rng) of (v, rng') -> (fromInteger (l + v `mod` k), rng') where k = h - l + 1 b = 2147483561 n = iLogBase b k
f 0 acc g = (acc, g) f n acc g = let (x,g') = next g in f (n-1) (fromIntegral x + acc * b) g'
iLogBase :: Integer -> Integer -> Integer iLogBase b i = if i < b then 1 else 1 + iLogBase b (i `div` b)
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