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Today's Topics:
1. Re: Re: Forcing evalation in the IO Monad (Philip Scott)
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Message: 1
Date: Fri, 16 Apr 2010 19:50:21 +0100
From: Philip Scott <[email protected]>
Subject: Re: [Haskell-beginners] Re: Forcing evalation in the IO Monad
To: Daniel Fischer <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
> Prelude Control.Exception> let lst = [undefined,undefined] :: [Bool]
> Prelude Control.Exception> evaluate lst>>= putStrLn . take 1 . show
> [
> Prelude Control.Exception> evaluate lst>>= print
> [*** Exception: Prelude.undefined
>
>
Ahh, yes you are of course right. Hmm so, how do we crack this nut
without resorting to deepSeq etc.. It must be possible, because it
happens when you print it!
Am I going to have to resort to physically writing the output to /dev/null ?
It seems like such an ordinary thing to want to do, the fact that it is
hard makes me think I must be approaching this in the wrong way (which
is usually the case when I get my knickers in a twist with Haskell ;)
- Phil
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End of Beginners Digest, Vol 22, Issue 30
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