Swap order of type arguments for BiMap in match and arrayOf functions

[chshersh]

Currently we have the following combinator:

data BiMap a b = BiMap
    { forward  :: a -> Maybe b
    , backward :: b -> Maybe a
    }

prism :: (object -> Maybe field) -> (field -> object) -> BiMap object field
prism preview review = BiMap preview (Just . review)

But usually it's used with invert function to get required type:

_Url :: BiMap Text Source
_Url = Toml.invert $ Toml.prism matchUrl Url

We need to add combinator like invert . prism but I don't know proper name for it 😞 The name should be short because it's going to be used often.

[jiegillet]

Why does the type need to be _Url :: BiMap Text Source rather than _Url :: BiMap Source Text?
Comparing :

Control.Lens.Prism._Left :: Prism (Either a c) (Either b c) a b
Toml._Left :: BiMap l (Either l r)

Control.Lens.Prism doesn't use an invert in the implementation.

[chshersh]

@jiegillet The reason for this is because prisms in tomland has two uses cases:

1. For array values:
   

   tomland/src/Toml/Bi/Combinators.hs

   Line 150 in 044de63

   arrayOf :: forall a . Typeable a => BiMap AnyValue a -> Key -> TomlCodec [a]

2. For parsing sum types with the help of match function
   

   tomland/src/Toml/Bi/Combinators.hs

   Line 58 in 044de63

   match :: forall a . Typeable a => BiMap AnyValue a -> Key -> TomlCodec a

Though, as I can see now, those functions can take BiMap a AnyValue instead of BiMap AnyValue a and there won't be any need in having inverted prism. Even if this is a quite serious breaking change, I think this is the way to go. I'd rather prefer consistency with the rest of the Haskell ecosystem and not have extra function.

[jiegillet]

I'll try to do the change. It might take a while, may the compiler be with me :)

[chshersh]

Closed in #106