Toml.Bi.Monad

Contains general underlying monad for bidirectional TOML converion.

Documentation

data Bijection r w c a

Monad for bidirectional Toml 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 Bi r w a = Bijection 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.

Constructors

Bijection

Fields

• biRead :: r a

  Extract value of type a from monadic context r.

• biWrite :: c -> w a

  Store value of type c inside monadic context w and returning value of type a. Type of this function actually should be a -> w () but with such type it's impossible to have Monad and other instances.

Instances

(Monad r, Monad w) => Monad (Bijection r w c)

Methods

(>>=) :: Bijection r w c a -> (a -> Bijection r w c b) -> Bijection r w c b

(>>) :: Bijection r w c a -> Bijection r w c b -> Bijection r w c b

return :: a -> Bijection r w c a

fail :: String -> Bijection r w c a

(Functor r, Functor w) => Functor (Bijection r w c)

Methods

fmap :: (a -> b) -> Bijection r w c a -> Bijection r w c b

(<$) :: a -> Bijection r w c b -> Bijection r w c a

(Applicative r, Applicative w) => Applicative (Bijection r w c)

Methods

pure :: a -> Bijection r w c a

(<*>) :: Bijection r w c (a -> b) -> Bijection r w c a -> Bijection r w c b

liftA2 :: (a -> b -> c) -> Bijection r w c a -> Bijection r w c b -> Bijection r w c c

(*>) :: Bijection r w c a -> Bijection r w c b -> Bijection r w c b

(<*) :: Bijection r w c a -> Bijection r w c b -> Bijection r w c a

type Bi r w a = Bijection r w a a

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

(.=) :: Bijection r w field a -> (object -> field) -> Bijection r w object a infixl 5

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