composite-dhall

ToDhall and FromDhall instances for composite records.

You lets you use extensible records over any base functor that is representable in dhall.

You can parse normal records:

{ a = "foo"
, b = +5 }

using a Record like:

withLensesAndProxies
  [d|
    type A = "a" :-> Text

    type B = "b" :-> Int
    |]

type MyRec = Record '[A, B]

This also works for Rec Maybe and Rec [].

{ a = Just "foo"
, b = Just +5 }

type MyMaybeRec = Rec Maybe '[A, B]

Similarly you can use a contravariant functor as the base functor to parse a collection of templates for different types.

{ a = \(x : Text) -> "Hello ${x}."
, b = \(y : Integer) -> "You are ${Integer/show y} years old."
}

newtype TextTemplate a = TextTemplate (Op Text a)
  deriving newtype (FromDhall)

newtype TextTemplates = TextTemplates {unTemplates :: Rec TextTemplate '[A, B]}
  deriving (FromDhall) via (Rec (Op Text) '[A, B])