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|
-----------------------------------------------------------------------------
-- |
-- Module : Debug.QuickCheck.Poly
-- Copyright : (c) Andy Gill 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : non-portable (uses Control.Exception, Control.Concurrent)
--
-- This is an attempt to emulate polymorphic types for the
-- purposes of testing by using abstract monomorphic types.
--
-- It is likely that future versions of QuickCheck will
-- include some polymorphic emulation testing facility,
-- but this module can be used for now.
--
-----------------------------------------------------------------------------
module Debug.QuickCheck.Poly
( ALPHA
, BETA
, GAMMA
, OrdALPHA
, OrdBETA
, OrdGAMMA
) where
import Prelude
import Debug.QuickCheck
import Debug.QuickCheck.Utils
{- This is the basic pseudo-polymorphic object.
- The idea is you can't cheat, and use the integer
- directly, but need to use the abstraction.
-
- We use phantom types (ref: Domain Specific Embedded Compilers,
- Daan Leijen & Erik Meijer, 2nd Conference of Domain Specific
- Languages, Austin, TX, 1999)
-}
newtype Poly a = Poly Int
instance Show (Poly a) where
show (Poly a) = "_" ++ show a
instance Arbitrary (Poly a) where
arbitrary = sized $ \n -> (choose (1,n) >>= return . Poly)
coarbitrary (Poly n) = variant (if n >= 0 then 2*n else 2*(-n) + 1)
instance Eq a => Eq (Poly a) where
(Poly a) == (Poly b) = a == b
instance Ord a => Ord (Poly a) where
(Poly a) `compare` (Poly b) = a `compare` b
{-
- These are what we export, our pseudo-polymorphic instances.
-}
type ALPHA = Poly ALPHA_
data ALPHA_ = ALPHA_ deriving (Eq)
type BETA = Poly BETA_
data BETA_ = BETA_ deriving (Eq)
type GAMMA = Poly GAMMA_
data GAMMA_ = GAMMA_ deriving (Eq)
type OrdALPHA = Poly OrdALPHA_
data OrdALPHA_ = OrdALPHA_ deriving (Eq,Ord)
type OrdBETA = Poly OrdBETA_
data OrdBETA_ = OrdBETA_ deriving (Eq,Ord)
type OrdGAMMA = Poly OrdGAMMA_
data OrdGAMMA_ = OrdGAMMA_ deriving (Eq,Ord)
{-
- This is a condition on OrdALPHA, OrdBETA, etc, itself.
- It states that all OrdALPHA objects obey total ordering.
-}
prop_OrdPOLY x y = isTotalOrder x y
where types = (x :: OrdALPHA, y :: OrdALPHA)
|
