Add a first example on how to use this library

Author: Pascal de Vink

examples/shorthand/README.md

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+# Parsing GraphQL IDL shorthand
+
+Shows how to build GraphQL schema from shorthand, wire up some resolvers, and add federation.
+
+### Run locally
+```
+php -S localhost:8080 ./graphql.php
+```
+
+### Try query
+```
+curl http://localhost:8080 -d '{"query": "query { echo(message: \"Hello World\") }" }'
+```
+
+### Try mutation
+```
+curl http://localhost:8080 -d '{"query": "mutation { sum(x: 2, y: 2) }" }'
+```
+
+### Try service sdl
+```
+curl http://localhost:8080 -d '{"query": "query {  _service {    sdl  } }" }'
+```
+
+### Try entities
+curl http://localhost:8080 -d '{"query":"query { _entities(representations: [{ __typename:\"User\", id:\"2\"}]) { __typename ... on User { id } } }","variables":{"_representations":[{"__typename":"User","id":"2"}]}}'

examples/shorthand/composer.json

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+{
+    "name": "pascaldevink/webonyx-implementation",
+    "require": {
+        "webonyx/graphql-php": "^0.13.8",
+        "pascaldevink/graphql-federation": "^0.1.0"
+    },
+    "autoload": {
+        "psr-4": {
+            "App\\": "src/"
+        }
+    },
+    "authors": [
+        {
+            "name": "Pascal de Vink",
+            "email": "pascal@ticketswap.com"
+        }
+    ]
+}

examples/shorthand/graphql.php

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+<?php
+
+// Test this using following command
+// php -S localhost:8080 ./graphql.php &
+// curl http://localhost:8080 -d '{"query": "query { echo(message: \"Hello World\") }" }'
+// curl http://localhost:8080 -d '{"query": "mutation { sum(x: 2, y: 2) }" }'
+require_once __DIR__ . '/../vendor/autoload.php';
+
+use GraphQL\GraphQL;
+use GraphQL\Utils\BuildSchema;
+
+try {
+    $originalSchema = BuildSchema::build(file_get_contents(__DIR__ . '/schema.graphqls'));
+
+    $federation = new \PascalDeVink\GraphQLFederation\Federation();
+    $schema = $federation->extendSchema($originalSchema);
+
+    $rootValue = include __DIR__ . '/rootvalue.php';
+    $rootValue = $federation->addResolversToRootValue($rootValue);
+
+    $rawInput = file_get_contents('php://input');
+    $input = json_decode($rawInput, true);
+    $query = $input['query'];
+    $variableValues = isset($input['variables']) ? $input['variables'] : null;
+
+    $result = GraphQL::executeQuery($schema, $query, $rootValue, null, $variableValues);
+} catch (\Exception $e) {
+    $result = [
+        'error' => [
+            'message' => $e->getMessage()
+        ]
+    ];
+}
+
+header('Content-Type: application/json; charset=UTF-8');
+echo json_encode($result);

examples/shorthand/rootvalue.php

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+<?php
+
+interface Resolver {
+    public function resolve($rootValue, $args, $context);
+}
+
+class Addition implements Resolver
+{
+    public function resolve($rootValue, $args, $context)
+    {
+        return $args['x'] + $args['y'];
+    }
+}
+
+class Echoer implements Resolver
+{
+    public function resolve($rootValue, $args, $context)
+    {
+        return $rootValue['prefix'].$args['message'];
+    }
+}
+
+return [
+    'sum' => function($rootValue, $args, $context) {
+        $sum = new Addition();
+
+        return $sum->resolve($rootValue, $args, $context);
+    },
+    'echo' => function($rootValue, $args, $context) {
+        $echo = new Echoer();
+
+        return $echo->resolve($rootValue, $args, $context);
+    },
+    'getUser' => function($rootValue, $args, $context) {
+        return [
+            'id' => 1,
+        ];
+    },
+    'prefix' => 'You said: ',
+];

examples/shorthand/schema.graphqls

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+schema {
+  query: Query
+  mutation: Mutation
+}
+
+type Mutation {
+  sum(x: Int, y: Int): Int
+}
+
+type Query {
+  echo(message: String): String
+#  getUser: User
+}
+
+type User @key(fields: "id") {
+  id: ID!
+}