Semigroup Result instance?

[hdgarrood]

How would we feel about the following?

instance semigroupResult :: Semigroup Result where
  Success <> r = r
  Failed str <> _ = Failed str

instance monoidResult :: Monoid Result where
  mempty = Success

This is a use case I have in mind

  log "fromRotationMatrix avoids instability issues when the quaternion has one very small component"
  quickCheck \(VerySmallNum e) a b c ->
    let
      testWith p' =
        let
          p = Rotation.fromQuaternion p'
          q = unsafePartial (Rotation.fromRotationMatrix (Rotation.toRotationMatrix p))
        in
          rApproxEq p q
          <?> show { p, q }
    in
      fold
       [ testWith (Quaternion e a b c)
       , testWith (Quaternion a e b c)
       , testWith (Quaternion a b e c)
       , testWith (Quaternion a b c e)
       ]

Of course I could rewrite this test to call quickCheck four times instead, but I think the instance makes sense, and I think it would be nice to allow writing tests this way. Additionally, if generating random values for a given type is expensive, being able to combine Result values in this way could let you cut down the number of random values you need to generate, since you don't need to call quickCheck as many times.

[garyb]

Seems reasonable to me!

[i-am-the-slime]

I came here asking for a Monoid instance. mempty could be Success, no?
Edit:
I just read the original post and it's there already.