Generic deriving for purescript-foreign.
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 = genericShowTo 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)))
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