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The safest way to generate random GADT with Hedgehog (or any other property-based testing framework)

I have a GADT, like this one:

data TType a where
    TInt  :: TType Int
    TBool :: TType Bool

I want to have a function like this:

genTType :: Gen (TType a)

May generate a random type constructor TType. I can do this simply by creating an existentially qualified data type, e.g.

data AnyType = forall a . MkAnyType (TType a)

then generate a random number from 0to 1(including) and create AnyTypedepending on the integer value. Like this:

intToAnyType :: Int -> AnyType
intToAnyType 0 = MkAnyType TInt
intToAnyType 1 = MkAnyType TBool
intToAnyType _ = error "Impossible happened"

But this approach has several drawbacks:

  • There is no external security. If I add another constructor to the data type TType, I may forget to fix the tests, and the compiler will not warn me about this.
  • The compiler cannot stop me from writing intToAnyType 1 = MkAnyType TInt.
  • error. Int . .

Haskell, ? :

+6
1

genTType Haskell, , , GADT .

oneof element.

 element [MkAnyType TInt, MkAnyType TBool]
+3

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