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hs-graphql

wip

components of the type system

types

This is the public api through which haskell data types may implement a GraphQL type of some kind. This is done by implementing an instance of GraphQLType:

newtype ID = ID String deriving (FromJSON, ToJSON)

instance GraphQLType ID where
  type KindOf ID = GraphQLScalar
  typename _ = "ID"

kinds

A graphql kind is a proxy type, such as the GraphQLScalar in the example above, that generally carries a dictionary of instances from its carrier type to be used for resolution and introspection. Type kinds can also be extended by implementing GraphQLKind, which translates its argument into a graphql type definition, and GraphQLTypeable which defines how to instantiate the proxy data type:

data GraphQLScalar a where
  Scalar :: (FromJSON a, ToJSON a) => Scalar a

instance GraphQLKind GraphQLScalar where
  type Kind GraphQLScalar = SCALAR
  typeDef Scalar = ScalarDef
instance (FromJSON a , ToJSON a) => GraphQLTypeable GraphQLScalar a where
  typeOf = Scalar

To plug its carrier type into an executable resolver it must further implement GraphQLInputKind, GraphQLOutputKind, or both depending on its Kind type. Such is the case for scalars:

instance GraphQLInputKind GraphQLScalar where
  readInputType Scalar = fromJSON
instance GraphQLOutputKind m GraphQLScalar where
  resolve Scalar = Leaf . toJson

todo

  • kinds
    • scalars
    • enums
    • objects
    • input objects
    • unions
    • interfaces
    • lists
    • nullable
  • parsing
  • validation
  • resolvers
    • resolve objects recursively
    • apply inputs
    • error handling
    • batching
    • subscriptions
  • root resolver
    • map operation types to their respective resolvers
    • extract all types defined in the resolvers recursively
  • schema introspection