[Ur] typechecker rejects form handler

[Sergey Mironov]

Hi. Could you please take a look at the program. Looks like
typechecker is wrong here. Full program is in attach, the faulty code
is below.
Thanks in advance,
Sergey

--

Faulty form handler:

fun form (sd:string) (fview : int -> url) (ferr : string -> url) :
transaction xbody =
  let
    fun retry {} : transaction page =
      redirect (ferr "Invalid form value")

    fun handler (s:{Text:string}) : transaction page =
      i <- nextval adv_s;
      dml(INSERT INTO adv (Id, Text) VALUES ({[i]}, {[s.Text]}));
      redirect (fview i)

    fun validator (s:{Text:string}) : transaction page =
      case s.Text != "" of
          True => handler s
        | False => retry {}

    (* Note: looks like it is the case expression who causes troubles.
Without it code works:
    fun validator (s:{Text:string}) : transaction page =
      handler s
    *)

  in
    return
      <xml>
        <form>
          <textarea{#Text}>
          {[sd]}
          </textarea>
          <br/>
          <submit action={validator}/>
        </form>
      </xml>
  end

The error message is

$ urweb -dbms sqlite FormBug
FormBug.ur:48:11: (to 48:17) Unification failure
Expression:  s.#Text
  Have con:  string
  Need con:
[<UNIF:U292::{<UNIF:U>}> ~ <UNIF:U293::{<UNIF:V>}>] =>
 <UNIF:U294::Type>
Incompatible constructors
Have:  string
Need:
[<UNIF:U292::{<UNIF:U>}> ~ <UNIF:U293::{<UNIF:V>}>] =>
 <UNIF:U294::Type>

Note, I am still using pre-released version of urweb, but I suppose it
doesn't meter here.
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