Ch13 - clarify exercise to "simplify the result of 'quickCheckPure'"

[shaunplee]

Chapter 13 has the following exercise, which was added in commit 46d5d2b:

4. (Medium) Use the all function to simplify the result of the quickCheckPure function - your function should return true if every test passes, and false otherwise. Try using the First monoid, defined in monoids with the foldMap function to preserve the first error in case of failure.

I am having trouble understanding this exercise. The first sentence makes it sound like the exercise is to write a function of type List Result -> Boolean using the all function.

However, it is unclear how to make this work with the second sentence, which asks that we try to "preserve the first error in case of failure" because I don't see how I can encode the first error in a Boolean.

Is the exercise asking the reader to write two functions, one with type List Result -> Boolean and another with type List Result -> First String?

Also, I can't seem to find a monoids package that includes a First newtype. (There seems to have been a monoid package that is now deprecated due to being merged into prelude.) Searching pursuit for "First," it seems like the First newtype from Data.Maybe.First is the monoid most similar to the one called for. If that's the case, then I can update the text to match.

[milesfrain]

All good points.
FYI, fixed a backtick / single-quote typo in your original post for readability.

I went into skim mode by the end of Ch13, so didn't get around to attempting that exercise, but I think a squashResults :: List Result -> Result is in the spirit of what it wants readers to do.

Doesn't look like foldMap will work with Data.Semigroup.First or Result, since there's no mempty/Monoid for those.
You could use Data.Maybe.First. There might be some even nicer ways to tackle this.

Also, it would be great if we could setup some exercise framework for this chapter. I was kinda stumped on what to do with this, since it's inverted where we're finally asking the readers to write the tests.

[milesfrain]

Also interesting that all-support for Result was proposed at one point, but doesn't follow the laws. purescript/purescript-quickcheck#101

[hdgarrood]

The Semigroup and Monoid instances there are fine, it was just the HeytingAlgebra instance which was problematic.