# Morpheus GraphQL [![Hackage](https://img.shields.io/hackage/v/morpheus-graphql.svg)](https://hackage.haskell.org/package/morpheus-graphql) ![CI](https://github.com/morpheusgraphql/morpheus-graphql/workflows/CI/badge.svg)

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](https://morpheus-graphql-slack-invite.herokuapp.com/) to get in touch.

Please note that this readme file provides only a brief introduction to the library. If you are interested in more advanced topics, visit [Docs](https://morpheusgraphql.com/).

## 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_

```yaml
dependencies:
  - morpheus-graphql
```

Additionally, you should tell stack which version to pick:

_stack.yml_

```yaml
resolver: lts-16.2

extra-deps:
  - morpheus-graphql-0.17.0
  - morpheus-graphql-app-0.17.0
  - morpheus-graphql-core-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

To define a GraphQL API with Morpheus we start by defining the API Schema as a native Haskell data type,
which derives the `Generic` type class. Using the `DeriveAnyClass` language extension we then also derive instances for the `GQLType` type class. 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`.

```haskell
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, GQLType)
```

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:

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

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.

```haskell
resolveDeity :: DeityArgs -> ResolverQ () IO 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:

```haskell
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:

```haskell
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`:

```GraphQL
query GetDeity {
  deity (name: "Morpheus") {
    fullName
    power
  }
}
```

our query will be resolved!

```JSON
{
  "data": {
    "deity": {
      "fullName": "Morpheus",
      "power": "Shapeshifting"
    }
  }
}
```