Hi Peter,<br><br>Thanks for asking about this issue.&nbsp; <br><br><blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote"><div>If I understood it correctly, it Conal&#39;s aim to provide just a
single integral function that can handle both the &nbsp;recursive and
regular cases?&nbsp;</div><div><br></div><div>But, is this even possible?</div></blockquote>

<div><br></div>Yes.&nbsp; The semantics of reactivity, plus the laziness of Haskell and some careful programming, makes it possible.&nbsp; I did it long ago in Fran.<br><br>Currently the implementation of snapshot (which integral uses) is not lazy enough for recursive snapshots to work.&nbsp; Chuan-kai Lin came up with a solution, which I think created a space leak.&nbsp; Richard Smith came up with essentially the same solution (and leak), and has been continuing to pursue a sufficiently lazy and space-tight.&nbsp; Today, Richard attached his patch to ticket # 14 on the Reactive tracker (<a href="http://trac.haskell.org/reactive/ticket/14">http://trac.haskell.org/reactive/ticket/14</a>).&nbsp; I&#39;ll check it out and integrate it if I think it will improve things.<br>
<br>In case anyone&#39;s curious, the crucial semantic decision is to have reactive behaviors change immediately after an event occurs.&nbsp; (Really immediately -- not some finite positive delay.)&nbsp; Thus an event can take a snapshot of a behavior at the moment that the behavior is reacting to that very event.&nbsp; The behavior and event are defined in terms of each other, in a well-defined and useful way.<br>
<br>&nbsp; - Conal<br><br><div class="gmail_quote">2008/12/2 Peter Verswyvelen <span dir="ltr">&lt;<a href="mailto:bugfact@gmail.com">bugfact@gmail.com</a>&gt;</span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
This has been brought up before, but I&#39;m not sure about the current status our consensus regarding &quot;recursive feedback&quot; in Reactive.<div><br></div><div>In Yampa this is solved by the ArrowLoop instance, and by having two different integral functions: one with a delay and without a delay.</div>


<div><br></div><div>If I understood it correctly, it Conal&#39;s aim to provide just a single integral function that can handle both the &nbsp;recursive and regular cases?&nbsp;</div><div><br></div><div>But, is this even possible?</div>


<div><br></div><div>A nice example of this is David&#39;s &quot;boingee&quot; example: a ball on the screen gets dragged towards the current mouse position.</div><div><br></div><div>Mathematically, this is</div><div><br>

</div><div>vb(t) = s * ( pm(t) - pb(t) )</div><div>pb(t) = pb0 + integral [0..t] vb(t)&nbsp;</div><div><br></div><div>where&nbsp;</div><div>&nbsp;&nbsp; pb(t) is the position of the ball at time t</div><div>&nbsp;&nbsp; pb0 is the initial position of the ball at time t=0,</div>

<div>&nbsp;&nbsp; pm(t) is the position of the mouse at time t</div><div>&nbsp;&nbsp; s is some arbitrary scale factor</div><div><br></div><div>Of course this is not really realistic but it is a simple example of recursive feedback: pb(t) depends on vb(t) and vice versa.</div>

<div><br></div><div>Can we make such behaviors with Reactive?</div><div><br></div><div><br></div><div><br></div>
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<br></blockquote></div><br>