Use hindent to automate formatting as much as we can

[harendra-kumar]

@Abhiroop I tried hindent --style johan-tibell --line-length 79 --indent-size 4 --sort-imports on Prelude.hs and the result is not much different from the existing style so I have no problem with whatever changes it suggests except the bug.

Bug

There is an unfixed bug in it that causes haddock to fail. Essentially it changes:

module Streamly.Prelude
    (
    -- * Construction
      nil
    , cons

To

module Streamly.Prelude
    -- * Construction
    ( nil
    , cons

Note the construction heading comment goes out which haddock does not like.

Stylistic differences

Other changes that differ from the current style, I can forget about the minor stuff in favor of full automation of formatting:

• it removes several blank lines that usually keep to have a better visible separation between comment sections and in the export list. I guess I can live with that.
• where has a two space indentation, which is fine I like that because where is more visible with this without loss of indentation.
• It changes single line signatures to multiline like this:

takeWhile :: Streaming t => (a -> Bool) -> t m a -> t m a

becomes

takeWhile
    :: Streaming t
    => (a -> Bool) -> t m a -> t m a

This is less compact but maybe a bit more readable (subjective), so accepted.

• Some manually aligned code gets unaligned e.g. this code was aligned on equal sign:

        yield a Nothing  = return (Just (a, nil))
        yield a (Just x) = return (Just (a, fromStream x))

It becomes:

        yield a Nothing = return (Just (a, nil))
        yield a (Just x) = return (Just (a, fromStream x))

• guards that were on a single line go to the next line:

        let yield a Nothing  | p a       = yld a Nothing
                             | otherwise = stp
            yield a (Just x) | p a       = yld a (Just (go x))
                             | otherwise = stp

becomes

            let yield a Nothing
                    | p a = yld a Nothing
                    | otherwise = stp
                yield a (Just x)
                    | p a = yld a (Just (go x))
                    | otherwise = stp

Not a big deal I guess.

• It does not keep DoAndIfThenElse style if-then-else:

        in if n1 <= 0
           then (runStream m1) ctx stp yld
           else (runStream m1) ctx stp yield

became

            in if n1 <= 0
                   then (runStream m1) ctx stp yld
                   else (runStream m1) ctx stp yield

I like the first style better.

• I tend to use if-then-else in a single line where it is possible:

            yield a (Just x) = if a == e then return True else go x

became

            yield a (Just x) =
                if a == e
                    then return True
                    else go x

I am ok with if it can at least follow the DoAndIfThenElse style.

• I use a let/in like this, where the ends of the keywords align not the beginning:

        let yield a Nothing  = return $ done a
         in (runStream m1) Nothing undefined yield

becomes

        let yield a Nothing = return $ done a
        in (runStream m1) Nothing undefined yield

Minor thing.

Conclusion

Other than the bug and the DoAndIfThenElse I am ok with the other changes. There is already an issue raised on hindent for the bug, maybe we can raise an issue for supporting the DoAndIfThenElse style.

@Abhiroop if you want to have a go at it you can submit a PR. If we change the style then it will be nice if we change all files to match the same style, it can be one at a time though.

[Abhiroop]

@harendra-kumar Yes I faced the module header bug last night when trying to build Abhiroop@351a378

[harendra-kumar]

Inactive.