In FsCheck, how to generate a test record with non-negative fields?

Question

In F#, I have a record with a few fields:

    type myRecord = { a:float; b:float; c:float }

I am using FsCheck to test some properties whic

Answer 1

Try this:

type Generators = 
    static member arbMyRecord =
        fun (a,b,c) -> { myRecord.a = a; b = b; c = c }
         (Arb.generate |> Gen.suchThat ((<) 0.) |> Gen.three)
        |> Arb.fromGen

Arb.register() |> ignore
Check.Quick verify_this_property

The is an infix map, useful for applicative style. This is an equivalent generator:

type Generators = 
    static member arbMyRecord =
        Arb.generate 
        |> Gen.suchThat ((<) 0.) 
        |> Gen.three
        |> Gen.map (fun (a,b,c) -> { myRecord.a = a; b = b; c = c })
        |> Arb.fromGen

If you don't want to globally register your generator, you can use forAll:

Check.Quick (forAll Generators.arbMyRecord verify_this_property)

Shrinking left as an exercise ;)