Documentation

Monad for bidirectional conversion. Contains pair of functions:

1. How to read value of type a from immutable environment context r?
2. How to store value of type a in stateful context w?

In practice instead of r we will use some Reader Toml and instead of w we will use State Toml. This approach with the bunch of utility functions allows to have single description for from/to Toml conversion.

In practice this type will always be used in the following way:

type BiCodec r w a = Codec r w a a

Type parameter c if fictional. Here some trick is used. This trick is implemented in codec and described in more details in related blog post.

Specialized version of Codec data type. This type alias is used in practice.

This is an instance of Profunctor for Codec. But since there's no Profunctor type class in base or package with no dependencies (and we don't want to bring extra dependencies) this instance is implemented as a single top-level function.

Useful when you want to parse newtypes. For example, if you had data type like this:

data Example = Example
    { foo :: Bool
    , bar :: Text
    }

toml bidirectional converter for this type will look like this:

exampleT :: TomlCodec Example
exampleT = Example
    $ bool "foo" .= foo
    * str  "bar" .= bar

Now if you change your time in the following way:

newtype Email = Email { unEmail :: Text }

data Example = Example
    { foo :: Bool
    , bar :: Email
    }

you need to patch your toml parser like this:

exampleT :: TomlCodec Example
exampleT = Example
    $ bool "foo" .= foo
    * dimap unEmail Email (str "bar") .= bar

Bidirectional converter for Maybe smth values.

Alternative instance for function arrow but without empty.

Operator to connect two operations:

1. How to get field from object?
2. How to write this field to toml?

In code this should be used like this:

data Foo = Foo { fooBar :: Int, fooBaz :: String }

foo :: TomlCodec Foo
foo = Foo
 $ int "bar" .= fooBar
 * str "baz" .= fooBaz