$ cat dune
(executable
 (name user)
 (libraries lwt caqti-lwt.unix caqti-driver-sqlite3 petrol)
 (preprocess
   (pps lwt_ppx)))

$ cat user.ml
open Petrol
open Petrol.Sqlite3

let version = VersionedSchema.version [ 1; 0; 0 ]
let schema = VersionedSchema.init version ~name:"user"

module User = struct
  let table, Expr.[ _id; username; password; is_admin ] =
    VersionedSchema.declare_table schema ~name:"user"
      Schema.
        [
          field
            ~constraints:[ primary_key ~auto_increment:true () ]
            "id" ~ty:Type.int;
          field "username" ~ty:Type.text;
          field "password" ~ty:Type.text;
          field "is_admin" ~ty:Type.bool;
        ]

  let insert (conn : Caqti_lwt.connection)  ~username:username'
      ~password:password' ~is_admin:is_admin' =
    Query.insert ~table
      ~values:
        Expr.
          [
            username := s username';
            password := s password';
            is_admin := bl is_admin';
          ]
    |> Request.make_zero |> Petrol.exec conn
end

let main =
  let uri_str = "sqlite3:./test-db.sqlite" in
  let uri = Uri.of_string uri_str in
    match%lwt Caqti_lwt_unix.connect uri with
    | Error _ -> Lwt.return ()
    | Ok conn ->
        match%lwt Petrol.VersionedSchema.initialise schema conn with
        | Error _ -> Lwt.return ()
        | Ok () -> User.insert conn ~username:"admin" ~password:"s3cr3t"
                     ~is_admin:true |> Lwt.map ignore


let () = Lwt_main.run main

$ dune exec ./user.exe
Fatal error: exception Failure("wrapped value list did not conform to specification - expected BOOLEAN got BOOLEAN")

$ echo '.schema' | sqlite3 ./test-db.sqlite 
CREATE TABLE petrol_user_version_db (version TEXT PRIMARY KEY NOT NULL);
CREATE TABLE user (id INTEGER PRIMARY KEY AUTOINCREMENT, username TEXT, password TEXT, is_admin BOOLEAN);
CREATE TABLE sqlite_sequence(name,seq);

$ echo 'select * from user;' | sqlite3 ./test-db.sqlite
# nothing...