[Haskell-cafe] Re: [Haskell-beginners] upgrade Hackage show to QuickCheck 2 for lambdabot

[Jonas Almström Duregård]

For some reason the generate function is not in QC2.

Here's a quick fix:

\begin{code}
import Test.QuickCheck.Gen
import System.Random

generate :: Int -> StdGen -> Gen a -> a
generate n rnd (MkGen m) = m rnd' size
  where
   (size, rnd') = randomR (0, n) rnd
\end{code}

Perhaps it would be better to ask the QC maintainers to re-include
this function in the library...

/Jonas

On 3 July 2010 01:09, Antoine Latter <aslatter at gmail.com> wrote:
> Including the café.
>
> On Jul 2, 2010 8:49 AM, "Mark Wright" <markwright at internode.on.net> wrote:
>
> Hi,
>
> I'm trying to upgrade Hackage show to QuickCheck 2, after
> applying the diffs below (which may not be correct, since I am
> a beginner), I am left which this error message:
>
> runghc ./Setup.hs build
> Preprocessing library show-0.3.4...
> Building show-0.3.4...
> [4 of 4] Compiling ShowQ            ( ShowQ.hs, dist/build/ShowQ.o )
>
> ShowQ.hs:104:20: Not in scope: `generate'
>
> Compilation exited abnormally with code 1 at Fri Jul  2 23:07:17
>
> The error occurs in this method:
>
> tests :: Gen Result -> StdGen -> Int -> Int -> [[String]] -> IO String
> tests gen rnd0 ntest nfail stamps
>  | ntest == 500  = done "OK, passed" ntest stamps
>  | nfail == 1000 = done "Arguments exhausted after" ntest stamps
>  | otherwise = case ok result of
>       Nothing    -> tests gen rnd1 ntest (nfail+1) stamps
>       Just True  -> tests gen rnd1 (ntest+1) nfail (stamp result:stamps)
>       Just False -> return $ "Falsifiable, after "
>                               ++ show ntest
>                               ++ " tests:\n"
>                               ++ reason result
>   where
>      result      = generate (((+ 3) . (`div` 2)) ntest) rnd2 gen
>      (rnd1,rnd2) = split rnd0
>
> The QuickCheck 1 generate method is near the bottom this page:
>
> http://hackage.haskell.org/packages/archive/QuickCheck/1.2.0.0/doc/html/Test-QuickCheck.html
>
> but I can not find generate in QuickCheck 2.  I am wondering if
> you have any ideas on how to fix it?
>
> I'm trying to package lambdabot on Solaris.  I have already packaged
> the Haskell Platform and about 90 packages, they are in:
>
> http://pkgbuild.sourceforge.net/spec-files-extra/
>
> Thanks very much, Mark
>
> here are the diffs:
>
> goanna% diff -wc show-0.3.4-orig/ShowQ.hs show-0.3.4/ShowQ.hs
> *** show-0.3.4-orig/ShowQ.hs    Wed Jan 20 11:24:11 2010
> --- show-0.3.4/ShowQ.hs Fri Jul  2 23:07:13 2010
> ***************
> *** 12,22 ****
> --- 12,25 ----
>
>  import qualified Test.SmallCheck (smallCheck, Testable)
>  import Test.QuickCheck
> + import Test.QuickCheck.Arbitrary
>  import Data.Char
>  import Data.List
>  import Data.Word
>  import Data.Int
>  import System.Random
> + import Control.Exception (evaluate)
> + import Test.QuickCheck.Property (ok, stamp)
>
>  type T = [Int]
>  type I = Int
> ***************
> *** 23,36 ****
> --- 26,45 ----
>
>  instance Arbitrary Char where
>      arbitrary     = choose (minBound, maxBound)
> +
> + instance CoArbitrary Char where
>      coarbitrary c = variant (ord c `rem` 4)
>
>  instance Arbitrary Word8 where
>      arbitrary = choose (minBound, maxBound)
> +
> + instance CoArbitrary Word8 where
>      coarbitrary c = variant (fromIntegral ((fromIntegral c) `rem` 4))
>
>  instance Arbitrary Ordering where
>      arbitrary     = elements [LT,EQ,GT]
> +
> + instance CoArbitrary Ordering where
>      coarbitrary LT = variant 1
>      coarbitrary EQ = variant 2
>      coarbitrary GT = variant 0
> ***************
> *** 37,42 ****
> --- 46,53 ----
>
>  instance Arbitrary Int64 where
>    arbitrary     = sized $ \n -> choose (-fromIntegral n,fromIntegral n)
> +
> + instance CoArbitrary Int64 where
>    coarbitrary n = variant (fromIntegral (if n >= 0 then 2*n else 2*(-n) +
> 1))
>
>  instance (Integral a, Arbitrary a) => Arbitrary (Ratio a) where
> ***************
> *** 48,53 ****
> --- 59,65 ----
>                              else (b % a)
>                           else (a % b)
>
> + instance (Integral a, CoArbitrary a) => CoArbitrary (Ratio a) where
>    coarbitrary m = variant (fromIntegral $ if n >= 0 then 2*n else 2*(-n) +
> 1)
>      where n = numerator m
>
> ***************
> *** 87,93 ****
>         Just False -> return $ "Falsifiable, after "
>                                 ++ show ntest
>                                 ++ " tests:\n"
> !                                ++ unlines (arguments result)
>     where
>        result      = generate (((+ 3) . (`div` 2)) ntest) rnd2 gen
>        (rnd1,rnd2) = split rnd0
> --- 99,105 ----
>         Just False -> return $ "Falsifiable, after "
>                                 ++ show ntest
>                                 ++ " tests:\n"
> !                                ++ reason result
>     where
>        result      = generate (((+ 3) . (`div` 2)) ntest) rnd2 gen
>        (rnd1,rnd2) = split rnd0
> goanna%
>
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