Add evalNF

[dcastro]

Added evalNF as discussed in #383.

A couple of things:

1. I created a local failException', which behaves exactly like failException except it also prints ━━━ Value could not be evaluated to normal form ━━━. Alternatively, we could simply change the type of failException to take an additional list of lines to be printed.

   -- before
   failException :: (MonadTest m, HasCallStack) => SomeException -> m a
   
   -- after
   failException :: (MonadTest m, HasCallStack) => [String] -> SomeException -> m a

   I suppose since failException is internal this would not be a breaking change, but still inconvenient... Any thoughts on whether we should refactor failException or leave the local bind for failException' in?
2. It wasn't clear to me how to add new tests for evalNF. I tried searching for tests for the existing eval, but couldn't find any. Should I add any tests and, if so, to which project/module?
3. I forgot to re-export either and either_ from Hedgehog.Gen in my previous PR, so I did that here, if that's OK. I can also submit this is a separate PR if you'd prefer.

[jacobstanley]

I'm ok with modifying the existing failException to take an argument given it's internal 👍

[jacobstanley]

It wasn't clear to me how to add new tests for evalNF. I tried searching for tests for the existing eval, but couldn't find any. Should I add any tests and, if so, to which project/module?

I think we don't have any tests for the evalXXX functions at the moment.

You could add a module to hedgehog-example if you're so inclined. Note that the tests in this project don't fail the build, all of the tests are failing on purpose to demonstrate how to use different features.

I'm cool with having no test though as it's so trivial.

[moodmosaic]

@jacobstanley @dcastro

I'm ok with modifying the existing failException to take an argument given it's internal 👍

Or even make a new top-level one called failExceptionWith taking a message, following the pattern used in all other xyzWith ones. Then have failException use the failExceptionWith one.

[moodmosaic]

Yep, basically we use eval in some of the examples via the assert one:

haskell-hedgehog/hedgehog/src/Hedgehog/Internal/Property.hs

Lines 726 to 732 in 4ec7254

	assert :: (MonadTest m, HasCallStack) => Bool -> m ()
	assert b = do
	ok <- withFrozenCallStack $ eval b
	if ok then
	success
	else
	withFrozenCallStack failure

Here's one of those examples:

haskell-hedgehog/hedgehog-example/src/Test/Example/Basic.hs

Lines 50 to 55 in 4ec7254

	prop_shrink_limit :: Property
	prop_shrink_limit =
	withShrinks 0 . property $ do
	x <- forAll $ Gen.enum 'a' 'z'
	assert $
	x == 'z'

[dcastro]

Thanks for the feedback!

I've added failExceptionWith, changed failException to use failExceptionWith, and added a couple of tests to hedgehog-example.

[moodmosaic]

👍

[moodmosaic]

Thank you, @dcastro!