Error in GraphQL examples

[Ecsodikas]

Hi everyone,

I was working through the graphql examples and I found out that the type system is not able to resolve all the types given in the example (https://github.com/aantron/dream/tree/master/example/i-graphql), so it does not compile.

open Graphql_lwt

type user = {id : int; name : string}

let hardcoded_users: user list = [
  {id = 1; name = "alice"};
  {id = 1; name = "bob"};
]

let user =
  Graphql_lwt.Schema.(obj "user"
    ~fields:[
      field "id"
        ~typ:(non_null int)
        ~args:Arg.[]
        ~resolve:(fun _info (user : user) -> user.id);
      field "name"
        ~typ:(non_null string)
        ~args:Arg.[]
        ~resolve:(fun _info (user : user) -> user.name);
    ])

let schema =
  Graphql_lwt.Schema.(schema [
    field "users"
      ~typ:(non_null (list (non_null user)))
      ~args:Arg.[arg "id" ~typ:int]
      ~resolve:(fun _info () id ->
        match id with
        | None -> hardcoded_users
        | Some id' ->
          match List.find_opt (fun {id; _} -> id = id') hardcoded_users with
          | None -> []
          | Some user -> [user]);
  ])

Produces the following error:

| let user =
         ^^^^
Error: The type of this expression,
       ('_weak1, user option) Graphql_lwt.Schema.typ,
       contains the non-generalizable type variable(s): '_weak1.
       (see manual section 6.1.2)

The solution is to make user and schema a function to solve the issue.