[Haskell-cafe] Hspec + QuickCheck passing type

[Will Yager]

I would recommend using http://hackage.haskell.org/package/base-4.8.2.0/docs/Prelude.html#v:asTypeOf

And passing a dummy variable of the correct type. 

-Will

> On Mar 28, 2016, at 12:53, Martijn Rijkeboer <haskell at bunix.org> wrote:
> 
> Hi,
> 
> I'm writing the following Hspec + QuickCheck test for some type:
> 
>  context "Type1" $
>    it "decode inverses encode" $ property $
>      \x -> (decode . encode) x == Right (x::Type1)
> 
> 
> However, I have a number of these types, and I could write the same test
> for every type, but that isn't very DRY. Therefore I would like to put the
> test in a function and call that function for every type. Something like
> the following:
> 
>  typeTest name = do
>    context name $
>      it "decode inverses encode" $ property $
>        \x -> (decode . encode) x == Right x
> 
> 
> Unfortunately this doesn't work, since QuickCheck doesn't know which
> Arbitrary instance to use. How can I pass the type, e.g. x::Type1, to
> this function so QuickCheck knows what Arbitrary instance to use?
> 
> Kind regards,
> 
> 
> Martijn Rijkeboer
> 
> 
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