graphql-meta
A GraphQL toolkit providing the following:
- Alex Lexer of the
GraphQLlexical specification. - Happy Parser of the
GraphQLBNF Grammar. - Pretty printer of the
GraphQLabstract syntax tree (AST) for human consumption. - QuickCheck generators for creating random AST fragments
- Used in conjunction with pretty printing to establish round trip property tests.
- Source
- Generics implementation providing correct-by-construction
Schemaat compile time. - QuasiQuoter providing inline definitions of
ExecutableDefinitions.
Table of Contents
Query
{-# LANGUAGE QuasiQuotes #-}
module Main (main) where
import GraphQL.QQ (query)
main :: IO ()
main = print [query| { building (id: 123) {floorCount, id}} |]Result
QueryDocument {getDefinitions = [
DefinitionOperation (AnonymousQuery [
SelectionField (Field Nothing (Name {unName = "building"}) [
Argument (Name {unName = "id"}) (ValueInt 123)] [] [
SelectionField (Field Nothing (Name {unName = "floorCount"}) [] [] [])
, SelectionField (Field Nothing (Name {unName = "id"}) [] [] [])
])
])
]}Substitution
GraphQL ExecutableDefinition abstract syntax tree rewriting is made possible via Template Haskell's metavariable substitution. During QuasiQuotation all unbound variables in a GraphQL query that have identical names inside the current scope will automatically be translated into GraphQL AST terms and substituted.
buildingQuery
:: Int
-> ExecutableDefinition
buildingQuery buildingId =
[query| { building (id: $buildingId) {floorCount, id}} |]Result
QueryDocument {getDefinitions = [
DefinitionOperation (AnonymousQuery [
SelectionField (Field Nothing (Name {unName = "building"}) [
Argument (Name {unName = "buildingId"}) (ValueInt 4)] [] [
SelectionField (Field Nothing (Name {unName = "floorCount"}) [] [] [])
, SelectionField (Field Nothing (Name {unName = "id"}) [] [] [])
])
])
]}Generics
It is possible to derive GraphQL schema using GHC.Generics.
Simply import GHC.Generics, derive Generic (must enable the DeriveGeneric language extension) and make an instance of ToObjectTypeDefintion.
See below for an example:
{-# LANGUAGE DeriveGeneric #-}
module Main where
import GHC.Generics (Generic)
import GraphQL.Internal.Syntax.Encoder (schemaDocument)
import Data.Proxy (Proxy)
import qualified Data.Text.IO as T
import GraphQL.Generic (ToObjectTypeDefinition(..))
data Person = Person
{ name :: String
, age :: Int
} deriving (Show, Eq, Generic)
instance ToObjectTypeDefinition Person
showPersonSchema :: IO ()
showPersonSchema = print $ toObjectTypeDefinition (Proxy @ Person)
-- type Person{name:String!,age:Int!}Limitations
- Generic deriving is currently only supported on product types with record field selectors.
- Only
ObjectTypeDefintionis currently supported.
Roadmap
- Generic deriving of
ScalarTypeDefintionandEnumTypeDefintion.
Maintainers
Credit
- Inspired by @edsko's work Quasi-quoting DLS for free.
AlexandHappylexing & parsing inspired by config-value
License
BSD3 2018-2019 Urbint Inc.