GraphQL in OCaml Tutorial

This repo contains the slides, code and exercises for the GraphQL in OCaml tutorial at CUFP 2017.

You can find the slides in the gh-pages-branch or browse them online.

Building and running the code

The code has been tested with OCaml 4.04.2 and the following versions of OPAM packages:

• graphql-lwt 0.3.0
• ppx_graphql 0.1.0
• jbuilder 1.0+beta11
• cohttp-lwt-unix 0.99.0
• tls 0.8.0
• opam-lib 1.3.1

You can achieve this with the following two commands:

opam switch 4.04.2
opam install graphql-lwt.0.3.0 ppx_graphql.0.1.0 jbuilder.1.0+beta11 cohttp-lwt-unix.0.99.0 tls.0.8.0 opam-lib.1.3.1

Running the Github CLI (exercise 3):

GITHUB_TOKEN=abc jbuilder build @github_cli

Running the GraphQL server (exercise 4 - 7):

GITHUB_TOKEN=abc jbuilder build @server --no-buffer

(GITHUB_TOKEN is only required from exercise 6 and onwards)

Now visit http://localhost:8080/graphql.

Documentation

• Graphql_lwt.Schema documentation
• andreas/ocaml-graphql-server
• andreas/ppx_graphql

Lwt Cheatsheet

module type Lwt = sig
  module Infix = sig
    val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
    val (>|=) : 'a t -> ('a -> 'b) -> 'b t
  end
end

module type Lwt_result = sig
  module Infix = sig
    val (>>=) : ('a, 'c) result Lwt.t ->
                ('a -> ('b, 'c) result Lwt.t) ->
                ('b, 'c) result Lwt.t

    val (>|=) : ('a, 'c) result Lwt.t ->
                ('a -> 'b) ->
                ('b, 'c) result Lwt.t
  end
end

(* Lwt.Infix example *)
let _ : string Lwt.t =
  let open Lwt.Infix in
  Lwt_io.(read_line_opt stdin) >|= function
  | None -> "No line read"
  | Some line -> "Line from stdin: %s" line

(* Lwt_result.Infix example *)
let _ : int result Lwt.t =
  let open Lwt_result.Infix in
  Lwt.return (Ok 41) >|= fun n ->
  n + 1

Exercise Solutions

You can find solutions to the exercises as git tags of this repo:

• Exercise 3 solutions
• Exercise 4 solutions
• Exercise 5 solutions
• Exercise 6 solutions
• Exercise 7 solutions