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Today's Topics:
1. Re: Seq question (Henk-Jan van Tuyl)
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Message: 1
Date: Thu, 19 Apr 2012 11:31:13 +0200
From: "Henk-Jan van Tuyl" <[email protected]>
Subject: Re: [Haskell-beginners] Seq question
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=iso-8859-15; format=flowed;
delsp=yes
On Wed, 18 Apr 2012 16:45:05 +0200, Brent Yorgey <[email protected]>
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
--
http://Van.Tuyl.eu/
http://members.chello.nl/hjgtuyl/tourdemonad.html
Haskell programming
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End of Beginners Digest, Vol 46, Issue 33
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