updated documentation strings to include empty tag in a union

[amkhlv]

The existing documentation on union decoder misses the case when one of constructors is an empty tag. This patch adds an example of that.

[Gabriella439]

I think this is what you want

[Gabriella439]

Suggested change

	adapt (Queued n) = Just (Left n)
	adapt (Result t) = Just (Right (Left t))
	adapt (Errored e) = Just (Right (Right e))
	adapt Unreachable = Nothing
	adapt (Queued n) = Left n
	adapt (Result t) = Right (Left t)
	adapt (Errored e) = Right (Right (Left e))
	adapt Unreachable = Right (Right (Right ()))

[Gabriella439]

Suggested change

	adapt (Queued n) = Just (Left n)
	adapt (Result t) = Just (Right (Left t))
	adapt (Errored e) = Just (Right (Right e))
	adapt Unreachable = Nothing
	adapt (Queued n) = Left n
	adapt (Result t) = Right (Left t)
	adapt (Errored e) = Right (Right (Left e))
	adapt Unreachable = Right (Right (Right ()))

[amkhlv]

I think I am getting a bit lost. The documentation on Hackage --- I think it is different from the docstring in the source file which I have been editing. Is this a newer version? What does the adapt function do?
That's why I wanted to compile it, to see the up-to-date documentation. But I could not compile it...

[Gabriella439]

Yeah, it's been a while since the last release to Hackage, which is the reason for the difference. However, I'm working on cutting a new release soon

[amkhlv]

Stackage would also be great. It would enable Hoogle...

[Gabriella439]

Suggested change

	| Unreachable ()
	| Unreachable

[amkhlv]

This is how I had it:

data DateFinished = Current () | Done DATE.Day | Dropped () deriving (Generic, Show, Eq)

and then:

dateFinishedDecoder :: Decoder DateFinished
dateFinishedDecoder =
  union
    ( (Current <$> constructor "Current" unit)
        <> (Done <$> constructor "Done" day)
        <> (Dropped <$> constructor "Dropped" unit)
    )

But if I do as you suggested, i.e. data DateFinished = Current | Done DATE.Day | Dropped deriving (Generic, Show, Eq) --- then it does not compile

[Gabriella439]

If you change that to:

dateFinishedDecoder :: Decoder DateFinished
dateFinishedDecoder =
  union
    ( (Current <$ constructor "Current" unit)  -- Carefully note the `<$`
        <> (Done <$> constructor "Done" day)
        <> (Dropped <$> constructor "Dropped" unit)
    )

… then it should compile

[amkhlv]

Oh, I got it ! Cute (although smells of witchcraft...). Then, maybe, instead of my suggested patch, would you rather write something pedagogical, in that docstring?

[amkhlv]

I just requested the pull for the correcting patch, as you suggested.