x = 1
 --> Value (Int 1)


 type alias X = Int
 --> TypeAlias [] Int


 type alias X a = Maybe a
 --> TypeAlias ["a"] (Maybe (Var 0))

Constructor of a custom type.

 type Foo = Bar
 --> CustomType [] [Constructor "Bar" []]


 type Foo a = Bar
 --> CustomType [] [Constructor "Bar" []]


 type Foo a = Bar a
 --> CustomType ["a"] [Constructor "Bar" ["a"]]


 type Foo = Bar | Baz
 --> CustomType []
        [ Constructor "Bar" []
        , Constructor "Baz" []
        ]

Apply a function to the expression inside the declaration.

Apply a function to the expression inside the declaration body.

Switch the Result and the expression inside the declaration body. Similar to Result.Extra.combine.

combine (Value (Ok (Int 5)))
--> Ok (Value (Int 5))