Extend Documentation Issue

[Tom Harding]

https://github.com/purescript/purescript-either/blob/master/src/Data/Either.purs#L161

Forgive me if I'm totally wrong (sorry!), but I think that line should be:

f <<= Right x = Right (f (Right x))

I know it's a relatively minor thing, but this issue is more to cement my understanding of the Extend class... Thanks!

[Gary Burgess]

It's right as it is actually, even though it may not appear so from the implementation!

extend ∷ ∀ w a b. Extend w ⇒ (w a → b) → w a → w b
extend ∷ ∀ a b. (Either e a → b) → Either e a → Either e b

Note how f expects an Either e a but returns a b. That's why we pass x (which is Right a) through without pattern matching on it. f then returns a value of b unwrapped, so we then re-wrap it to produce a Right b result.

[Tom Harding]

I see, though wouldn't f <<= Right x = Right (f x) suggest that x is the value within the Right? Sorry, I'm probably missing something obvious!

[Gary Burgess]

Hah, sorry, yes you are absolutely right after all.

[Tom Harding]

Fixed in #22 at long last - closing :)