morpheus-graphql
Morpheus GraphQL
| Version on this page: | 0.17.0 |
| LTS Haskell 23.28: | 0.28.1 |
| Stackage Nightly 2025-05-05: | 0.28.1 |
| Latest on Hackage: | 0.28.1 |
morpheus-graphql-0.17.0@sha256:487ad2e2b11d1038a65068f139f291a4e7b00986c347132b56e141608f0c8789,29450Module documentation for 0.17.0
Morpheus GraphQL 
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
Setup
To get started with Morpheus, you first need to add it to your project’s dependencies, as follows (assuming you’re using hpack):
package.yml
dependencies:
- morpheus-graphql
Additionally, you should tell stack which version to pick:
stack.yml
resolver: lts-16.2
extra-deps:
- 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
schema.gql
type Query {
deity(name: String! = "Morpheus"): Deity!
}
"""
Description for Deity
"""
type Deity {
"""
Description for name
"""
name: String!
power: String @deprecated(reason: "some reason for")
}
API.hs
{-# 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 =
RootResolver
{ queryResolver = Query {deity},
mutationResolver = Undefined,
subscriptionResolver = Undefined
}
where
deity DeityArgs {name} =
pure
Deity
{ 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 =
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") {
fullName
power
}
}
our query will be resolved!
{
"data": {
"deity": {
"fullName": "Morpheus",
"power": "Shapeshifting"
}
}
}
Serverless Example
If you are interested in creating a Morpheus GraphQL API with Serverless, you should take a look at our example in this repository:
Mythology API it is our example project build with Morpheus GraphQL and Serverless-Haskell,
where you can query different mythology characters with GraphiQL.
Mythology API is deployed on : api.morpheusgraphql.com where you can test it with GraphiQL
Advanced topics
Enums
You can use Union Types as Enums, but they’re not allowed to have any parameters.
data City
= Athens
| Sparta
| Corinth
| Delphi
| Argos
deriving (Generic)
instance GQLType City where
type KIND City = ENUM
Union types
To use union type, all you have to do is derive the GQLType class. Using GraphQL fragments, the arguments of each data constructor can be accessed from the GraphQL client.
data Character
= CharacterDeity Deity -- will be unwrapped, since Character + Deity = CharacterDeity
| SomeDeity Deity -- will be wrapped since Character + Deity != SomeDeity
| Creature { creatureName :: Text, creatureAge :: Int }
| Demigod Text Text
| Zeus
deriving (Generic, GQLType)
where Deity is an object.
As we see, there are different kinds of unions. Morpheus handles them all.
This type will be represented as
union Character = Deity | SomeDeity | Creature | SomeMulti | Zeus
type SomeDeity {
_0: Deity!
}
type Creature {
creatureName: String!
creatureAge: Int!
}
type Demigod {
_0: Int!
_1: String!
}
type Zeus {
_: Unit!
}
By default, union members will be generated with wrapper objects. There is one exception to this: if a constructor of a type is the type name concatenated with the name of the contained type, it will be referenced directly. That is, given:
data Song = { songName :: Text, songDuration :: Float } deriving (Generic, GQLType)
data Skit = { skitName :: Text, skitDuration :: Float } deriving (Generic, GQLType)
data WrappedNode
= WrappedSong Song
| WrappedSkit Skit
deriving (Generic, GQLType)
data NonWrapped
= NonWrappedSong Song
| NonWrappedSkit Skit
deriving (Generic, GQLType)
You will get the following schema:
# has wrapper types
union WrappedNode = WrappedSong | WrappedSkit
# is a direct union
union NonWrapped = Song | Skit
type WrappedSong {
_0: Song!
}
type WrappedSKit {
_0: Skit!
}
type Song {
songDuration: Float!
songName: String!
}
type Skit {
skitDuration: Float!
skitName: String!
}
-
for all other unions will be generated new object type. for types without record syntax, fields will be automatically indexed.
-
all empty constructors in union will be summed in type
<tyConName>Enum(e.gCharacterEnum), this enum will be wrapped inCharacterEnumObjectand added to union members.
Scalar types
To use custom scalar types, you need to provide implementations for parseValue and serialize respectively.
data Odd = Odd Int deriving (Generic)
instance DecodeScalar Euro where
decodeScalar (Int x) = pure $ Odd (... )
decodeScalar _ = Left "invalid Value!"
instance EncodeScalar Euro where
encodeScalar (Odd value) = Int value
instance GQLType Odd where
type KIND Odd = SCALAR
Applicative and Monad instance
The Resolver type has Applicative and Monad instances that can be used to compose resolvers.
Introspection
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 provide an implementation for the description function:
data Deity = Deity
{ ...
} deriving (Generic)
instance GQLType Deity where
description = const "A supernatural being considered divine and sacred"
screenshots from Insomnia
Handling Errors
for errors you can use use either liftEither or MonadFail:
at the and they have same result.
with liftEither
resolveDeity :: DeityArgs -> ResolverQ e IO Deity
resolveDeity DeityArgs {} = liftEither $ dbDeity
dbDeity :: IO Either Deity
dbDeity = pure $ Left "db error"
with MonadFail
resolveDeity :: DeityArgs -> ResolverQ e IO Deity
resolveDeity DeityArgs { } = fail "db error"
Mutations
In addition to queries, Morpheus also supports mutations. They behave just like regular queries and are defined similarly:
newtype Mutation m = Mutation
{ createDeity :: MutArgs -> m Deity
} deriving (Generic, GQLType)
rootResolver :: RootResolver IO () Query Mutation Undefined
rootResolver =
RootResolver
{ queryResolver = Query {...}
, mutationResolver = Mutation { createDeity }
, subscriptionResolver = Undefined
}
where
-- Mutation Without Event Triggering
createDeity :: MutArgs -> ResolverM () IO Deity
createDeity_args = lift setDBAddress
gqlApi :: ByteString -> IO ByteString
gqlApi = interpreter rootResolver
Subscriptions
In morpheus subscription and mutation communicate with Events,
Event consists with user defined Channel and Content.
Every subscription has its own Channel by which it will be triggered
data Channel
= ChannelA
| ChannelB
data Content
= ContentA Int
| ContentB Text
type MyEvent = Event Channel Content
newtype Query m = Query
{ deity :: m Deity
} deriving (Generic)
newtype Mutation m = Mutation
{ createDeity :: m Deity
} deriving (Generic)
newtype Subscription (m :: * -> * ) = Subscription
{ newDeity :: m Deity
} deriving (Generic)
newtype Subscription (m :: * -> *) = Subscription
{ newDeity :: SubscriptionField (m Deity),
}
deriving (Generic)
type APIEvent = Event Channel Content
rootResolver :: RootResolver IO APIEvent Query Mutation Subscription
rootResolver = RootResolver
{ queryResolver = Query { deity = fetchDeity }
, mutationResolver = Mutation { createDeity }
, subscriptionResolver = Subscription { newDeity }
}
where
-- Mutation Without Event Triggering
createDeity :: ResolverM EVENT IO Address
createDeity = do
requireAuthorized
publish [Event { channels = [ChannelA], content = ContentA 1 }]
lift dbCreateDeity
newDeity :: SubscriptionField (ResolverS EVENT IO Deity)
newDeity = subscribe ChannelA $ do
-- executed only once
-- immediate response on failures
requireAuthorized
pure $ \(Event _ content) -> do
-- executes on every event
lift (getDBAddress content)
Interface
-
defining interface with Haskell Types (runtime validation):
-- interface is just regular type derived as interface newtype Person m = Person {name :: m Text} deriving (Generic) instance GQLType (Person m) where type KIND (Person m) = INTERFACE -- with GQLType user can links interfaces to implementing object instance GQLType Deity where implements _ = [interface (Proxy @Person)] -
defining with
importGQLDocumentandDSL(compile time validation):interface Account { name: String! } type User implements Account { name: String! }
Morpheus GraphQL Client with Template haskell QuasiQuotes
defineByDocumentFile
"./schema.gql"
[gql|
query GetHero ($character: Character)
{
deity (fatherOf:$character) {
name
power
worships {
deity2Name: name
}
}
}
|]
with schema:
input Character {
name: String!
}
type Deity {
name: String!
worships: Deity
power: Power!
}
enum Power {
Lightning
Teleportation
Omniscience
}
will validate query and Generate:
- namespaced response and variable types
- instance for
FetchtypeClass
data GetHero = GetHero {
deity: DeityDeity
}
-- from: {user
data DeityDeity = DeityDeity {
name: Text,
worships: Maybe DeityWorshipsDeity
power: Power
}
-- from: {deity{worships
data DeityWorshipsDeity = DeityWorshipsDeity {
name: Text,
}
data Power =
PowerLightning
| PowerTeleportation
| PowerOmniscience
data GetHeroArgs = GetHeroArgs {
character: Character
}
data Character = Character {
name: Person
}
as you see, response type field name collision can be handled with GraphQL alias.
with fetch you can fetch well typed response GetHero.
fetchHero :: Args GetHero -> m (Either String GetHero)
fetchHero = fetch jsonRes args
where
args = GetHeroArgs {character = Person {name = "Zeus"}}
jsonRes :: ByteString -> m ByteString
jsonRes = <GraphQL APi>
in this case, jsonRes resolves a request into a response in some monad m.
A fetch resolver implementation against a real API may look like the following:
{-# LANGUAGE OverloadedStrings #-}
import Data.ByteString.Lazy (ByteString)
import qualified Data.ByteString.Char8 as C8
import Network.HTTP.Req
resolver :: String -> ByteString -> IO ByteString
resolver tok b = runReq defaultHttpConfig $ do
let headers = header "Content-Type" "application/json"
responseBody <$> req POST (https "swapi.graph.cool") (ReqBodyLbs b) lbsResponse headers
this is demonstrated in examples/src/Client/StarWarsClient.hs
types can be generated from introspection too:
defineByIntrospectionFile "./introspection.json"
Morpheus CLI for Code Generating
you should use morpheus-graphql-cli
Showcase
Below are the list of projects using Morpheus GraphQL. If you want to start using Morpheus GraphQL, they are good templates to begin with.
- https://github.com/morpheusgraphql/mythology-api
- Serverless Mythology API
- https://github.com/dandoh/web-haskell
- Modern webserver boilerplate in Haskell: Morpheus Graphql + Postgresql + Authentication + DB migration + Dotenv and more
Edit this section and send PR if you want to share your project.
About
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.
Team
Morpheus is written and maintained by nalchevanidze
Roadmap
- Medium future:
- Stabilize API
- Specification-isomorphic error handling
- Long term:
- Support all possible GQL features
- Performance optimization