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    Yes, JavaScript functions are not valid as functions within Ur/Web's
    runtime representations.  The details are intentionally
    undocumented, but perhaps I should add more of a disclaimer not to
    rely on the details.  (I hope I've understood your issue report well
    enough to isolate the problem.)<br>
    <br>
    <div class="moz-cite-prefix">On 05/22/2017 01:53 PM, Aistis
      Raulinaitis wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAKzB5bVKhCh10ObWEpy-=EAabw=U8LSWQacT8x8eLWc8soDKnQ@mail.gmail.com">
      <div dir="ltr">
        <div>Ah, so is this now why I'm getting this error?: TypeError:
          fr.f is not a function<br>
          <br>
        </div>
        <div>Here's some screenshots of the code in the inspector: <a
            href="http://imgur.com/a/FBm3R" moz-do-not-send="true">http://imgur.com/a/FBm3R</a><br>
        </div>
        <div><br>
        </div>
        <div>The code in question looks like this:<br>
          <br>
          function new_map_with (init) {<br>
              var acc = new Map ();<br>
              var curr = init;<br>
              while (curr._2 != null) {<br>
                  acc.set (curr._1._1, curr._1._2);<br>
                  curr = curr._2;}<br>
              //curr._1._1 contains the last elem when curr._1._2 ===
          null.<br>
              acc.set (curr._1._1, curr._1._2);<br>
              return acc;}<br>
        </div>
        <div><br>
        </div>
        I am attempting to pass back the Map from JS back to Ur, and it
        seems that fr.f at runtime will hold new_map_with at first, then
        after it executes it then holds the Map I generates. At that
        point line 1991 gets called e = {c: "c", v: fr.f(v)}; and I get
        that error, since fr.f now holds Map {...} and Map isn't a
        function..<br>
      </div>
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Mon, May 22, 2017 at 4:42 AM, Adam
          Chlipala <span dir="ltr"><<a
              href="mailto:adamc@csail.mit.edu" target="_blank"
              moz-do-not-send="true">adamc@csail.mit.edu</a>></span>
          wrote:<br>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <div text="#000000" bgcolor="#FFFFFF">
              <div class="m_-170248232430822086moz-cite-prefix">I can
                confirm that non-primitive/abstract types are not meant
                to cross the FFI boundary.
                <div>
                  <div class="h5"><br>
                    <br>
                    On 05/21/2017 11:31 PM, Aistis Raulinaitis wrote:<br>
                  </div>
                </div>
              </div>
              <div>
                <div class="h5">
                  <blockquote type="cite">
                    <div dir="ltr">Thanks!<br>
                    </div>
                    <div class="gmail_extra"><br>
                      <div class="gmail_quote">On Sun, May 21, 2017 at
                        8:27 PM, Artyom Shalkhakov <span dir="ltr"><<a
                            href="mailto:artyom.shalkhakov@gmail.com"
                            target="_blank" moz-do-not-send="true">artyom.shalkhakov@gmail.com</a>></span>
                        wrote:<br>
                        <blockquote class="gmail_quote" style="margin:0
                          0 0 .8ex;border-left:1px #ccc
                          solid;padding-left:1ex"><span>2017-05-22 9:19
                            GMT+06:00 Aistis Raulinaitis <<a
                              href="mailto:sheganinans@gmail.com"
                              target="_blank" moz-do-not-send="true">sheganinans@gmail.com</a>>:<br>
                            > Hmm, that makes sense. Do you have an
                            example of FFI with an abstract type?<br>
                            > I tried to encapsulate the map type
                            with a con, but obviously that does not<br>
                            > work..<br>
                            ><br>
                            <br>
                          </span>Sure, here are two examples:<br>
                          <br>
                          <a
                            href="https://github.com/bbarenblat/urweb-regex"
                            rel="noreferrer" target="_blank"
                            moz-do-not-send="true">https://github.com/bbarenblat/<wbr>urweb-regex</a>
                          (in particular, take a look<br>
                          at regex__FFI.urs and the two types
                          [substring_t] and<br>
                          [substring_list_t])<br>
                          <a
                            href="https://github.com/ashalkhakov/urweb-storage"
                            rel="noreferrer" target="_blank"
                            moz-do-not-send="true">https://github.com/ashalkhakov<wbr>/urweb-storage</a>
                          (shameless plug; in<br>
                          particular, take a look at storage__FFI.urs
                          and the type [storage])<br>
                          <div class="m_-170248232430822086HOEnZb">
                            <div class="m_-170248232430822086h5"><br>
                              > On Sun, May 21, 2017 at 8:10 PM,
                              Artyom Shalkhakov<br>
                              > <<a
                                href="mailto:artyom.shalkhakov@gmail.com"
                                target="_blank" moz-do-not-send="true">artyom.shalkhakov@gmail.com</a>>
                              wrote:<br>
                              >><br>
                              >> 2017-05-22 6:22 GMT+06:00 Aistis
                              Raulinaitis <<a
                                href="mailto:sheganinans@gmail.com"
                                target="_blank" moz-do-not-send="true">sheganinans@gmail.com</a>>:<br>
                              >> > So I am working with the JS
                              FFI, however it seems that the clientOnly<br>
                              >> > directive is being ignored.<br>
                              >> ><br>
                              >> > Here is the example code:<br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > main.urp:<br>
                              >> > ~~~<br>
                              >> ><br>
                              >> > ffi js_map<br>
                              >> > jsFunc
                              Js_map.new_map=new_map<br>
                              >> > jsFunc
                              Js_map.new_map_with=new_map_wi<wbr>th<br>
                              >> > clientOnly Js_map.new_map<br>
                              >> > clientOnly
                              Js_map.new_map_with<br>
                              >> > benignEffectful
                              Js_map.new_map<br>
                              >> > benignEffectful
                              Js_map.new_map_with<br>
                              >> > jsFile js_map.js<br>
                              >> ><br>
                              >> > main<br>
                              >> ><br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > main.urs:<br>
                              >> > ~~~<br>
                              >> ><br>
                              >> > val main : unit ->
                              transaction page<br>
                              >> ><br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > main.ur:<br>
                              >> > ~~~<br>
                              >> ><br>
                              >> > fun main () =<br>
                              >> >     c <-
                              Js_map.new_map_with ((1, 2)::[]);<br>
                              >> >     return
                              <xml></xml><br>
                              >> ><br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > js_map.urs:<br>
                              >> > ~~~<br>
                              >> ><br>
                              >> > con js_map :: Type ->
                              Type -> Type<br>
                              >> ><br>
                              >> > val new_map      : k :::
                              Type -> v ::: Type -> unit ->
                              transaction<br>
                              >> > (js_map k<br>
                              >> > v)<br>
                              >> > val new_map_with : k :::
                              Type -> v ::: Type -> list (k * v)
                              -><br>
                              >> > transaction<br>
                              >> > (js_map k v)<br>
                              >> ><br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > js_map.js:<br>
                              >> > ~~~<br>
                              >> ><br>
                              >> > function new_map () {return
                              new Map ();}<br>
                              >> ><br>
                              >> > function new_map_with (arg)
                              {return new Map (arg); }<br>
                              >> ><br>
                              >> ><br>
                              >> > ~~~<br>
                              >> > So in main.ur, you can see
                              that I am calling this Js code in a C<br>
                              >> > context,<br>
                              >> > instead of getting an error
                              complaining about how it should be called
                              on<br>
                              >> > the<br>
                              >> > client, instead I get this
                              confusing error:<br>
                              >> ><br>
                              >> > urweb main<br>
                              >> >
                              /Users/ace/src/cli_only/js_map<wbr>.urs:4:75:
                              (to 4:87) Unsupported type<br>
                              >> > constructor<br>
                              >> > Constructor: 
                              FFI(Js_map.js_map_with) FFI(Basis.int)
                              FFI(Basis.int)<br>
                              >> >
                              /usr/local/Cellar/urweb/201701<wbr>05/lib/urweb/ur/basis.urs:127:<wbr>23:
                              (to<br>
                              >> > 127:25)<br>
                              >> > Unsupported type constructor<br>
                              >> > Constructor: 
                              FFI(Js_map.js_map_with) FFI(Basis.int)
                              FFI(Basis.int)<br>
                              >> > make: *** [all] Error 1<br>
                              >> ><br>
                              >><br>
                              >> I got the impression that Ur/Web
                              being a whole-program optimizing<br>
                              >> compiler, the only types being
                              supported for marshalling between FFI<br>
                              >> code and non-FFI code are
                              primitive types and abstract types. I
                              think<br>
                              >> I asked this same question some
                              time ago.<br>
                              >><br>
                              >> So it looks like you will have to
                              work around this somehow.<br>
                              >><br>
                              >> ><br>
                              >> ><br>
                              >> >
                              ______________________________<wbr>_________________<br>
                              >> > Ur mailing list<br>
                              >> > <a
                                href="mailto:Ur@impredicative.com"
                                target="_blank" moz-do-not-send="true">Ur@impredicative.com</a><br>
                              >> > <a
                                href="http://www.impredicative.com/cgi-bin/mailman/listinfo/ur"
                                rel="noreferrer" target="_blank"
                                moz-do-not-send="true">http://www.impredicative.com/c<wbr>gi-bin/mailman/listinfo/ur</a><br>
                              >> ><br>
                              >><br>
                              >><br>
                              >><br>
                              >> --<br>
                              >> Cheers,<br>
                              >> Artyom Shalkhakov<br>
                              >><br>
                              >> ______________________________<wbr>_________________<br>
                              >> Ur mailing list<br>
                              >> <a
                                href="mailto:Ur@impredicative.com"
                                target="_blank" moz-do-not-send="true">Ur@impredicative.com</a><br>
                              >> <a
                                href="http://www.impredicative.com/cgi-bin/mailman/listinfo/ur"
                                rel="noreferrer" target="_blank"
                                moz-do-not-send="true">http://www.impredicative.com/c<wbr>gi-bin/mailman/listinfo/ur</a><br>
                              ><br>
                              ><br>
                              ><br>
                              > ______________________________<wbr>_________________<br>
                              > Ur mailing list<br>
                              > <a
                                href="mailto:Ur@impredicative.com"
                                target="_blank" moz-do-not-send="true">Ur@impredicative.com</a><br>
                              > <a
                                href="http://www.impredicative.com/cgi-bin/mailman/listinfo/ur"
                                rel="noreferrer" target="_blank"
                                moz-do-not-send="true">http://www.impredicative.com/c<wbr>gi-bin/mailman/listinfo/ur</a><br>
                              ><br>
                              <br>
                              <br>
                              <br>
                              --<br>
                              Cheers,<br>
                              Artyom Shalkhakov<br>
                              <br>
                              ______________________________<wbr>_________________<br>
                              Ur mailing list<br>
                              <a href="mailto:Ur@impredicative.com"
                                target="_blank" moz-do-not-send="true">Ur@impredicative.com</a><br>
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                                href="http://www.impredicative.com/cgi-bin/mailman/listinfo/ur"
                                rel="noreferrer" target="_blank"
                                moz-do-not-send="true">http://www.impredicative.com/c<wbr>gi-bin/mailman/listinfo/ur</a><br>
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</pre>
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