Make Gen.eval easier to use in v3

[moodmosaic]

Currently, the type signature of Gen.eval is

int -> StdGen -> Gen<'a> -> 'a

Where int stands for size, StdGen for an instance of Random, and Gen<'a> for the generator we want to evaluate.

I believe that StdGen shouldn't be exposed, as it's really an implementation detail, and so Gen.eval should look like:

int -> Gen<'a> -> 'a

Where int stands for size, and Gen<'a> for the generator we want to evaluate.

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If Runner uses Gen.eval for test-replaying, that could be done via some other function, probably internal, or hidden.

Related: #267, #236, #198.

[Aaronontheweb]

I second this - would help a lot with an FsCheck integration I'm working on designed to make it much easier to use with C# POCO classes (including fun edge cases like constructor arguments, etc...). Being able to access the same StdGen instance as the Runner or not having to worry about it period would be great.

[moodmosaic]

Actually, I think that making Gen.eval public wasn't a good idea at all, since there's Gen.sample...

[ploeh]

Isn't Gen.eval deterministic?

[moodmosaic]

True. Gen.sample uses Gen.eval internally. And Gen.eval takes the seed as argument so it's an easy way to replay a test... I've updated my comment above.

[moodmosaic]

👍