CODEWITHSUNDEEP
haskellquickcheck
Cliff Stamp
Cliff Stamp

Reputation: 571

Codewars (Haskell random testing QuickCheck)

I have this working code in the random testing part of a Kata:

it "handles randoms " $ 
      property $ \x y -> updateHealth x y == if y > x then 0 else x-y

But I wanted the function signature to use Num, but when I did that I get an error because (I believe) it doesn't know how to generate Nums (as it doesn't know what kind of Nums to make?). I just hard set the type to Double as a work around.

However is there a way to use Quickcheck when your function signature uses Nums? Do you have to tell it specifically to generate random Int, or Integer, Float or Double?

Upvotes: 1

Views: 158

Answers (1)

Gabriel L.
Gabriel L.

Reputation: 1709

However is there a way to use Quickcheck when your function signature uses Nums? Do you have to tell it specifically to generate random Int, or Integer, Float or Double?

As @AJFarmar states, Num is a type class (family of types), not a specific type.

You CAN use QuickCheck with a function like Num a => a -> a -> a, you just have to specialize the type through annotation. You can either annotate the updateHealth function or else annotate the property function itself:

it "handles randoms " $ 
  property $ \x y -> (updateHealth :: Int -> Int -> Int) x y == if y > x then 0 else x-y

(or)

it "handles randoms " $ 
  property ((\x y -> updateHealth x y == if y > x then 0 else x-y) :: Int -> Int -> Bool)

These options are preferable to changing updateHealth's type at its definition; you want your functions to stay general, so you can specialize them at their call sites if necessary.

Upvotes: 1

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