Morpheus GraphQL

Code Gen

Morpheus GraphQL Hackage CI

Build GraphQL APIs with your favorite functional language!

Morpheus GraphQL (Server & Client) helps you to build GraphQL APIs in Haskell with native Haskell types. Morpheus will convert your Haskell types to a GraphQL schema and all your resolvers are just native Haskell functions. Morpheus GraphQL can also convert your GraphQL Schema or Query to Haskell types and validate them in compile time.

Morpheus is still in an early stage of development, so any feedback is more than welcome, and we appreciate any contribution! Just open an issue here on GitHub, or join our Slack channel to get in touch.

Getting Started


To get started with Morpheus, you first need to add it to your project's dependencies, as follows (assuming you're using hpack):


  - morpheus-graphql

Additionally, you should tell stack which version to pick:


resolver: lts-16.2

  - morpheus-graphql-0.17.0

As Morpheus is quite new, make sure stack can find morpheus-graphql by running stack upgrade and stack update

Building your first GraphQL API

with GraphQL syntax


type Query {
  deity(name: String! = "Morpheus"): Deity!

Description for Deity
type Deity {
  Description for name
  name: String!
  power: String @deprecated(reason: "some reason for")


{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

module API (api) where

import Data.ByteString.Lazy.Char8 (ByteString)
import Data.Morpheus (interpreter)
import Data.Morpheus.Document (importGQLDocument)
import Data.Morpheus.Types (RootResolver (..), Undefined (..))
import Data.Text (Text)

importGQLDocument "schema.gql"

rootResolver :: RootResolver IO () Query Undefined Undefined
rootResolver =
    { queryResolver = Query {deity},
      mutationResolver = Undefined,
      subscriptionResolver = Undefined
    deity DeityArgs {name} =
          { name = pure name,
            power = pure (Just "Shapeshifting")

api :: ByteString -> IO ByteString
api = interpreter rootResolver

Template Haskell Generates types: Query , Deity, DeityArgs, that can be used by rootResolver

descriptions and deprecations will be displayed in introspection.

importGQLDocumentWithNamespace will generate Types with namespaced fields. If you don't need namespace use importGQLDocument

with Native Haskell Types

To define a GraphQL API with Morpheus we start by defining the API Schema as a native Haskell data type, which derives the Generic typeClass. Lazily resolvable fields on this Query type are defined via a -> ResolverQ () IO b, representing resolving a set of arguments a to a concrete value b.

data Query m = Query
  { deity :: DeityArgs -> m Deity
  } deriving (Generic, GQLType)

data Deity = Deity
  { fullName :: Text         -- Non-Nullable Field
  , power    :: Maybe Text   -- Nullable Field
  } deriving (Generic,GQLType)

data DeityArgs = DeityArgs
  { name      :: Text        -- Required Argument
  , mythology :: Maybe Text  -- Optional Argument
  } deriving (Generic)

For each field in the Query type defined via a -> m b (like deity) we will define a resolver implementation that provides the values during runtime by referring to some data source, e.g. a database or another API. Fields that are defined without a -> m b you can just provide a value.

In above example, the field of DeityArgs could also be named using reserved identities (such as: type, where, etc), in order to avoid conflict, a prime symbol (') must be attached. For example, you can have:

data DeityArgs = DeityArgs
  { name      :: Text        -- Required Argument
  , mythology :: Maybe Text  -- Optional Argument
  , type'     :: Text
  } deriving (Generic)

The field name in the final request will be type instead of type'. The Morpheus request parser converts each of the reserved identities in Haskell 2010 to their corresponding names internally. This also applies to selections.

resolveDeity :: DeityArgs -> ResolverQ e () Deity
resolveDeity DeityArgs { name, mythology } = liftEither $ dbDeity name mythology

askDB :: Text -> Maybe Text -> IO (Either String Deity)
askDB = ...

To make this Query type available as an API, we define a RootResolver and feed it to the Morpheus interpreter. A RootResolver consists of query, mutation and subscription definitions, while we omit the latter for this example:

rootResolver :: RootResolver IO () Query Undefined Undefined
rootResolver =
    { queryResolver = Query {deity = resolveDeity}
    , mutationResolver = Undefined
    , subscriptionResolver = Undefined

gqlApi :: ByteString -> IO ByteString
gqlApi = interpreter rootResolver

As you can see, the API is defined as ByteString -> IO ByteString which we can either invoke directly or use inside an arbitrary web framework such as scotty or serverless-haskell. We'll go for scotty in this example:

main :: IO ()
main = scotty 3000 $ post "/api" $ raw =<< (liftIO . gqlApi =<< body)

If we now send a POST request to http://localhost:3000/api with a GraphQL Query as body for example in a tool like Insomnia:

query GetDeity {
  deity(name: "Morpheus") {

our query will be resolved!

  "data": {
    "deity": {
      "fullName": "Morpheus",
      "power": "Shapeshifting"

Advanced topics


Morpheus converts your schema to a GraphQL introspection automatically. You can use tools like Insomnia to take a look at the introspection and validate your schema. If you need a description for your GQLType inside of the introspection you can define the GQLType instance manually and apply Describe directive to it:

data Deity = Deity
{ ...
} deriving (Generic)

instance GQLType Deity where
  directives _ = typeDirective (Describe "A supernatural being considered divine and sacred")

screenshots from Insomnia

alt text alt text alt text


The name

Morpheus is the greek god of sleep and dreams whose name comes from the Greek word μορφή meaning form or shape. He is said to be able to mimic different forms and GraphQL is good at doing exactly that: Transforming data in the shape of many different APIs.


Morpheus is written and maintained by nalchevanidze


  • Medium future:
    • Stabilize API
    • Specification-isomorphic error handling
  • Long term:
    • Support all possible GQL features
    • Performance optimization