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updated documentation strings to include empty tag in a union #2625

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updated documentation strings to include empty tag in a union #2625

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51de0d6
updated documentation strings to include the case of empty tag in a u…
Jan 4, 2025
b779323
Merge branch 'main' into main
winitzki Jan 5, 2025
ad2f8f9
docs for union decoder: changed Maybe to Either and the type of Unrea…
Jan 5, 2025
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18 changes: 12 additions & 6 deletions dhall/src/Dhall/Marshal/Encode.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -943,6 +943,7 @@ encodeFieldWith name encodeType = RecordEncoder $ Dhall.Map.singleton name encod
data Status = Queued Natural
| Result Text
| Errored Text
| Unreachable ()
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Suggested change
| Unreachable ()
| Unreachable

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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

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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

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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?

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

:}

And assume that we have the following Dhall union that we would like to
Expand All @@ -951,6 +952,7 @@ data Status = Queued Natural
> < Result : Text
> | Queued : Natural
> | Errored : Text
> | Unreachable
> >.Result "Finish successfully"

Our encoder has type 'Encoder' @Status@, but we can't build that out of any
Expand All @@ -963,11 +965,13 @@ injectStatus = adapt >$< unionEncoder
( encodeConstructorWith "Queued" inject
>|< encodeConstructorWith "Result" inject
>|< encodeConstructorWith "Errored" inject
>|< encodeConstructorWith "Unreachable" inject
)
where
adapt (Queued n) = Left n
adapt (Result t) = Right (Left t)
adapt (Errored e) = Right (Right e)
adapt (Queued n) = Just (Left n)
adapt (Result t) = Just (Right (Left t))
adapt (Errored e) = Just (Right (Right e))
adapt Unreachable = Nothing
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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 ()))

:}

Or, since we are simply using the `ToDhall` instance to inject each branch, we could write
Expand All @@ -978,11 +982,13 @@ injectStatus = adapt >$< unionEncoder
( encodeConstructor "Queued"
>|< encodeConstructor "Result"
>|< encodeConstructor "Errored"
>|< encodeConstructor "Unreachable"
)
where
adapt (Queued n) = Left n
adapt (Result t) = Right (Left t)
adapt (Errored e) = Right (Right e)
adapt (Queued n) = Just (Left n)
adapt (Result t) = Just (Right (Left t))
adapt (Errored e) = Just (Right (Right e))
adapt Unreachable = Nothing
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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 ()))

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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...

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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

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

:}

-}
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