Henk-Jan van Tuly is correct. Oops! Sorry I was mis-informed. By the way, there is an excellent post about this topic on StackOverflow.com. It covers, seq, weak-head-normal-form, normal form, and thunks. See here:<div><a href="http://stackoverflow.com/questions/6872898/haskell-what-is-weak-head-normal-form/6889335#6889335">http://stackoverflow.com/questions/6872898/haskell-what-is-weak-head-normal-form/6889335#6889335</a> </div>
<div><br></div><div>Hope that makes up for my earlier comment.</div><div><br></div><div>Tim<br><div><br><br><div class="gmail_quote">On Thu, Apr 19, 2012 at 2:31 AM, Henk-Jan van Tuyl <span dir="ltr"><<a href="mailto:hjgtuyl@chello.nl">hjgtuyl@chello.nl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On Wed, 18 Apr 2012 16:45:05 +0200, Brent Yorgey <<a href="mailto:byorgey@seas.upenn.edu" target="_blank">byorgey@seas.upenn.edu</a>> wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Tue, Apr 17, 2012 at 02:41:15PM -0700, Tim Perry wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
seq evaluates to Weak Head Normal Form (WHNF). WHNF is the first<br>
contructor. So your use of seq only evaluates the first number and the<br>
cons. I.E., it evaluates to:<br>
s:(Thunk)<br>
</blockquote>
<br>
Actually, it doesn't even force the first number. You just get<br>
<br>
Thunk : Thunk<br>
<br>
</blockquote>
<br></div>
A nice way to demonstrate this, is the following GHCi session:<br>
Prelude> undefined `seq` print "OK"<br>
*** Exception: Prelude.undefined<br>
Prelude> [undefined] `seq` print "OK"<br>
"OK"<br>
<br>
<br>
Regards,<br>
Henk-Jan van Tuyl<span class="HOEnZb"><font color="#888888"><br>
<br>
<br>
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