<br><font size=2 face="sans-serif">but there's no risk using trace is there?</font>
<br>
<br><font size=2 face="sans-serif">t.</font>
<br>
<br><font size=2 face="sans-serif">> </font><tt><font size=2>The unsafe...
functions are called that<br>
for a reason, and their use should be highly discouraged,<br>
except in cases where there is absolutely no other<br>
reasonable way. </font></tt>
<br>
<br>
<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>"Yitzchak Gale"
<gale@sefer.org></b> </font>
<br><font size=1 face="sans-serif">Sent by: haskell-cafe-bounces@haskell.org</font>
<p><font size=1 face="sans-serif">11/29/2007 05:01 PM</font>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">"Andrew Coppin" <andrewcoppin@btinternet.com></font>
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<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
<td><font size=1 face="sans-serif">haskell-cafe@haskell.org</font>
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<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [Haskell-cafe] Progress indications</font></table>
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<br>
<br><tt><font size=2>Bit Connor wrote:<br>
> computation is. And since it's all calls to map and filter et al.,
it's<br>
> ...it's not immediately clear how to provide any feedback<br>
> on how much longer there is to wait.<br>
<br>
Andrew Coppin wrote:<br>
> It seems unsafePerformIO is the way to go here.<br>
> ...unsafeInterleaveIO<br>
<br>
I disagree. The unsafe... functions are called that<br>
for a reason, and their use should be highly discouraged,<br>
except in cases where there is absolutely no other<br>
reasonable way. I don't believe that this is one<br>
of those cases.<br>
<br>
A better approach is to use pure monads. Instead of<br>
<br>
f :: ... -> a<br>
<br>
write functions whose type is something like<br>
<br>
f :: ... -> MyMonad a<br>
<br>
where MyMonad is defined in one and only<br>
one place in your program. Or, better yet,<br>
polymorphic things like<br>
<br>
f :: Monad m => ... -> m a<br>
f :: MyMonadClass m => ... -> m a<br>
<br>
Then when you later need to add something<br>
like progress indicators, you just add that<br>
to the capabilities of your monad, and add<br>
some updateProgress calls to your functions.<br>
By using "do" notation wisely, you can<br>
keep your abstractions just as clear as they<br>
were, and cleanly separated from the progress logic.<br>
<br>
Other things you may need to add later in<br>
real-world programs are exception handling,<br>
logging, trace, etc. All of these are easy if you<br>
started out in a monad.<br>
<br>
-Yitz<br>
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</font></tt>
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