con colMeta = fn (db :: Type, widget :: Type) =>
                 {Nam : string,
                  Show : db -> xbody,
                  Widget : nm :: Name -> xml form [] [nm = widget],
                  WidgetPopulated : nm :: Name -> db -> xml form [] [nm = widget],
                  Parse : widget -> db,
                  Inject : sql_injectable db}
con colsMeta = fn cols :: {(Type * Type)} => $(map colMeta cols)

fun default [t] (sh : show t) (rd : read t) (inj : sql_injectable t)
            name : colMeta (t, string) =
    {Nam = name,
     Show = txt,
     Widget = fn [nm :: Name] => <xml><textbox{nm}/></xml>,
     WidgetPopulated = fn [nm :: Name] n =>
                          <xml><textbox{nm} value={show n}/></xml>,
     Parse = readError,
     Inject = _}

val int = default
val float = default
val string = default

fun bool name = {Nam = name,
                 Show = txt,
                 Widget = fn [nm :: Name] => <xml><checkbox{nm}/></xml>,
                 WidgetPopulated = fn [nm :: Name] b =>
                                      <xml><checkbox{nm} checked={b}/></xml>,
                 Parse = fn x => x,
                 Inject = _}

functor Make(M : sig
                 con cols :: {(Type * Type)}
                 constraint [Id] ~ cols
                 val fl : folder cols

                 table tab : ([Id = int] ++ map fst cols)

                 val title : string

                 val cols : colsMeta cols
             end) = struct

    val tab = M.tab

    sequence seq

    fun list () =
        rows <- queryX (SELECT * FROM tab AS T)
                       (fn (fs : {T : $([Id = int] ++ map fst M.cols)}) => <xml>
                         <tr>
                           <td>{[fs.T.Id]}</td>
                           {@foldRX2 [fst] [colMeta] [tr]
                             (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                                              [[nm] ~ rest] v col => <xml>
                                                <td>{col.Show v}</td>
                                              </xml>)
                             M.fl (fs.T -- #Id) M.cols}
                           <td>
                             <a link={upd fs.T.Id}>[Update]</a>
                             <a link={confirm fs.T.Id}>[Delete]</a>
                           </td>
                         </tr>
                       </xml>);
        return <xml>
          <table border={1}>
            <tr>
              <th>ID</th>
              {@foldRX [colMeta] [tr]
                (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                                 [[nm] ~ rest] col => <xml>
                                   <th>{cdata col.Nam}</th>
                                 </xml>)
                M.fl M.cols}
            </tr>
            {rows}
          </table>

          <br/><hr/><br/>

          <form>
            {@foldR [colMeta] [fn cols :: {(Type * Type)} => xml form [] (map snd cols)]
              (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                               [[nm] ~ rest] (col : colMeta t) (acc : xml form [] (map snd rest)) => <xml>
                                 <li> {cdata col.Nam}: {col.Widget [nm]}</li>
                                 {useMore acc}
                               </xml>)
              <xml/>
              M.fl M.cols}
            
            <submit action={create}/>
          </form>
        </xml>

    and create (inputs : $(map snd M.cols)) =
        id <- nextval seq;
        dml (insert tab
                    (@foldR2 [snd] [colMeta]
                      [fn cols => $(map (fn t :: (Type * Type) =>
                                            sql_exp [] [] [] t.1) cols)]
                      (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                                       [[nm] ~ rest] =>
                       fn input col acc => acc ++ {nm = @sql_inject col.Inject (col.Parse input)})
                      {} M.fl inputs M.cols
                     ++ {Id = (SQL {[id]})}));
        ls <- list ();
        return <xml><body>
          <p>Inserted with ID {[id]}.</p>

          {ls}
        </body></xml>

    and upd (id : int) =
        let
            fun save (inputs : $(map snd M.cols)) =
                dml (update [map fst M.cols]
                            (@foldR2 [snd] [colMeta]
                              [fn cols => $(map (fn t :: (Type * Type) =>
                                                    sql_exp [T = [Id = int]
                                                                     ++ map fst M.cols]
                                                            [] [] t.1) cols)]
                              (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                                               [[nm] ~ rest] =>
                               fn input col acc => acc ++ {nm =
                                                           @sql_inject col.Inject (col.Parse input)})
                              {} M.fl inputs M.cols)
                            tab (WHERE T.Id = {[id]}));
                ls <- list ();
                return <xml><body>
                  <p>Saved!</p>

                  {ls}
                </body></xml>
        in
            fso <- oneOrNoRows (SELECT tab.{{map fst M.cols}} FROM tab WHERE tab.Id = {[id]});
            case fso : (Basis.option {Tab : $(map fst M.cols)}) of
                None => return <xml><body>Not found!</body></xml>
              | Some fs => return <xml><body><form>
                {@foldR2 [fst] [colMeta] [fn cols :: {(Type * Type)} => xml form [] (map snd cols)]
                  (fn [nm :: Name] [t :: (Type * Type)] [rest :: {(Type * Type)}]
                                   [[nm] ~ rest] (v : t.1) (col : colMeta t)
                                   (acc : xml form [] (map snd rest)) =>
                      <xml>
                        <li> {cdata col.Nam}: {col.WidgetPopulated [nm] v}</li>
                        {useMore acc}
                      </xml>)
                  <xml/>
                  M.fl fs.Tab M.cols}

                <submit action={save}/>
              </form></body></xml>
        end

    and confirm (id : int) =
        let
            fun delete () =
                dml (DELETE FROM tab WHERE Id = {[id]});
                ls <- list ();
                return <xml><body>
                  <p>The deed is done.</p>
                  
                  {ls}
                </body></xml>
        in
            return <xml><body>
              <p>Are you sure you want to delete ID #{[id]}?</p>
              
              <form><submit action={delete} value="I was born sure!"/></form>
            </body></xml>
        end    

    and main () =
        ls <- list ();
        return <xml><head>
          <title>{cdata M.title}</title>
        </head><body>

          <h1>{cdata M.title}</h1>

          {ls}
        </body></xml>

end