gabiseabra / hs-graphql

[WIP] An experimental library for deriving GraphQL schema documents, parsing requests and type-checking them against the schema, and executing the requests against Haskell handlers compatible with the type declarations, all inferred from Haskell types and compliant with GraphQL specs.

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