[plt-scheme] Fr. Time questions

From: Gregory Cooper (greg at cs.brown.edu)
Date: Fri Sep 17 11:38:18 EDT 2004

> 1.  Dr. Scheme is still freezing regularly when I use Fr. Time.  It

I haven't witnessed this myself, though I don't use Windows.  I'm not sure
if it's a bug in FrTime, or FrTime exposing a bug in [the Windows version
of] DrScheme.  While it's definitely a serious issue, I don't have any
clear leads about where to look, at least for the moment.  Sorry.  :-(

> 2.  Is there a way to have the dynamic updating pause and resume?  Or
> perhaps ensure that several operations are atomic vs one update of the
> clock?  I've written some code to simulate gravity with a planet

Posting code would probably help, though I'll be out of town and with
limited network access for a couple of weeks.  A more recent version of
FrTime might help some, either from CVS or from


However, if the problem is really that you need to synchronize the main
thread (which creates the signals) with the FrTime engine (which updates
the signals), then the solution may be a bit more complicated, though
certainly possible.

> 3.  snapshot and value seem to freeze everything recursively.  For
> example, the following code:

The problem is really that FrTime's cons flattens a list of behaviors into
a monolithic behavior.  (I've decided that this is not the way it should
work, and fixing it is near the top of my priority list.)  For now, a
simple fix might be to use the primitive MzScheme cons:

(require (rename mzscheme mz:cons cons))

(and replace every cons with mz:cons)

I hope this helps.  Also, feel free to take the last two points off the
list (if you want) and send follow-up questions directly to me.


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