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    <p>You can register a callback that, when called, reads another
      callback out of a [source] and calls it.  Is that sufficient?<br>
    </p>
    <div class="moz-cite-prefix">On 11/10/2017 04:19 PM, Nitin Surana
      wrote:<br>
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cite="mid:CAOX1NxuRSd=JQeiq4v07gk4AhLEg+sfNHoB8c5=fFx9xCkv34g@mail.gmail.com">
      <div dir="ltr">Hi Adam
        <div><br>
        </div>
        <div>Thanks for responding. Is there any alternative to change
          the callback ? I want to trigger a urweb function defined
          within `let` block upon a javascript event. </div>
        <div>Since, the function is within `let` block (because it needs
          access to certain variables within the parent function), I'm
          unable to use execF(...) from javascript.</div>
        <div><br>
        </div>
        <div>Also, is `ref` not supported in urweb ?</div>
        <div><br>
        </div>
        <div>Thanks</div>
      </div>
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Fri, Nov 10, 2017 at 4:48 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"><span class="">
                <div class="m_5243511948070250283moz-cite-prefix">On
                  11/09/2017 10:42 PM, Harshita Kasera wrote:<br>
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                  <div dir="ltr"><span style="font-size:12.8px"></span>
                    <div style="font-size:12.8px">
                      <div style="font-size:12.8px">What I ultimately
                        want to achieve is to be able to change the
                        callback function <i>debugMe</i> at a later
                        point of time. Is it possible to set or update
                        values within a structure at a later point of
                        time?</div>
                    </div>
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                </blockquote>
                <br>
              </span> No, module (structure) fields can't be modified at
              runtime in Ur/Web or ML.  Therefore, the module system is
              not the right tool for runtime rewriting of callbacks.<br>
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