[Haskell-cafe] ghc overlapping instances -> solved

[Steffen Mazanek]

Hello,

Isaac, this works for me.

Thx a lot,

Steffen





2007/12/5, Isaac Dupree <isaacdupree at charter.net>:
>
> Steffen Mazanek wrote:
> > Hi,
> >
> > Stefan and Isaac, thx for providing quick advice.
> >
> > @Stefan: Unfortunately I have to use a list.
> > @Isaac: I do not get it. Could you please provide a short example of
> your
> > approach?
> >
> > The question still remains. Which arguments do I have ghc to start with
> to
> > get the same behavior than hugs with -98 +o (here it works).
> >
> > I provide my example for testing purposes:
> >
> > module Test where
> > import Test.QuickCheck
> > import Monad(liftM,liftM2)
> >
> > type Program = [Stmt]
> > data Stmt = Text | IfElse Program Program | While Program deriving (Eq,
> > Show)
> >
> > instance Arbitrary [Stmt] where
> >   arbitrary = sized genProg
> > instance Arbitrary Stmt where
> >   arbitrary = sized genStmt
> >
> > genStmt::Int->Gen Stmt
> > genStmt 0 = return Text
> > genStmt 1 = return Text
> > genStmt 2 = oneof [return Text, return (While [Text])]
> > genStmt n | n>2 = oneof ([return Text,
> >                           liftM While (genProg (n-1))]++
> >                          [liftM2 IfElse (genProg k) (genProg
> > (n-k-1))|k<-[1..n-2]])
> >
> > genProg::Int->Gen Program
> > genProg 0 = return []
> > genProg 1 = return [Text]
> > genProg n | n>1 = oneof ((liftM (\x->[x]) (genStmt n)):[liftM2 (:)
> (genStmt
> > k) (genProg (n-k))|k<-[1..n-1]])
> >
> > prop_ConstructParse progr = True
> >   where types = progr::Program
> >
> > main = mapM_ (\(s,a) -> putStrLn s >> a) [("flowchart construct and
> parse",
> > test prop_ConstructParse)]
>
> is prop_ConstructParse the only thing that breaks when you remove the
> instance Arbitrary [Stmt] where arbitrary = sized genProg, or have I
> missed something?  If that's all, try this (untested) :
>
> prop_ConstructParse = forAll (sized genProg) (\progr -> True)
>
> and similarly for other properties.
>
> Or, you _can_ use a newtype for quickcheck-only, something like this:
>
> newtype P = P { unP :: Program }
> instance Show P where show = show . unP
> instance Arbitrary P where arbitrary = sized genProg . unP
> prop_ConstructParse (P progr) = True
>
>
> Isaac
>



-- 
Dipl.-Inform. Steffen Mazanek
Institut für Softwaretechnologie
Fakultät Informatik

Universität der Bundeswehr München
85577 Neubiberg

Tel: +49 (0)89 6004-2505
Fax: +49 (0)89 6004-4447

E-Mail: steffen.mazanek at unibw.de
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