purescript-foreign-generic

Generic deriving for purescript-foreign.

Example Usage

First, define some data type and derive Generic:

> import Prelude
> import Data.Generic.Rep (class Generic)
> import Data.Generic.Rep.Show (genericShow)

> newtype MyRecord = MyRecord { a :: Int }
> derive instance genericMyRecord :: Generic MyRecord _
> instance showMyRecord :: Show MyRecord where show = genericShow

To encode JSON, use genericEncodeJSON:

> import Data.Foreign.Class (class Encode, class Decode, encode, decode)
> import Data.Foreign.Generic (defaultOptions, genericDecodeJSON, genericEncodeJSON)

> opts = defaultOptions { unwrapSingleConstructors = true }

> genericEncodeJSON opts (MyRecord { a: 1 })
"{\"a\":1}"

And to decode JSON, use genericDecodeJSON:

> import Control.Monad.Except

> runExcept (genericDecodeJSON opts "{\"a\":1}" :: _ MyRecord)
(Right (MyRecord { a: 1 }))

Badly formed JSON will result in a useful error, which can be inspected or pretty-printed:

> lmap (map renderForeignError) $ runExcept (genericDecodeJSON opts "{\"a\":\"abc\"}" :: _ MyRecord)
(Left
  (NonEmptyList
    (NonEmpty
      "Error at array index 0: (ErrorAtProperty \"a\" (TypeMismatch \"Int\" \"String\"))"
      Nil)))