Re: [Haskell-beginners] Seq question

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: http://stackoverflow.com/questions/6872898/haskell-what-is-weak-head-normal-... Hope that makes up for my earlier comment. Tim On Thu, Apr 19, 2012 at 2:31 AM, Henk-Jan van Tuyl wrote:

On Wed, 18 Apr 2012 16:45:05 +0200, Brent Yorgey wrote:

On Tue, Apr 17, 2012 at 02:41:15PM -0700, Tim Perry wrote:

...

...

seq evaluates to Weak Head Normal Form (WHNF). WHNF is the first contructor. So your use of seq only evaluates the first number and the cons. I.E., it evaluates to: s:(Thunk)

Actually, it doesn't even force the first number. You just get

Thunk : Thunk

A nice way to demonstrate this, is the following GHCi session: Prelude> undefined `seq` print "OK" *** Exception: Prelude.undefined Prelude> [undefined] `seq` print "OK" "OK"

Regards, Henk-Jan van Tuyl

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