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Today's Topics:
1. list doesn't end (Alexander Chen)
2. Re: list doesn't end (Oliver Charles)
3. Re: list doesn't end (Francesco Ariis)
----------------------------------------------------------------------
Message: 1
Date: Sat, 23 Nov 2019 19:38:03 +0100 (CET)
From: Alexander Chen <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] list doesn't end
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Hi,
I am doing some further learning with euler now in Haskell instead of Julia.
But I am getting something strange.
[x+y+z | x <- a2, y <- b3, z <- c4, (x+y+z) < 50]
a2, b3, c4 are all finite lists derived from the lazy list of the primes
package. the output is:
[28,47,33,49
this is not a typo it is still calculating hence the missing bracket (for the
last couple of hours, when to a christmas fair in between). The only thing is
that, this should be the answer:
[28,47,33,49]
so it should be done but its not. what am I doing wrong?
best,
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Message: 2
Date: Sat, 23 Nov 2019 18:42:05 +0000
From: Oliver Charles <[email protected]>
To: Alexander Chen <[email protected]>, The Haskell-Beginners
Mailing List - Discussion of primarily beginner-level topics related
to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] list doesn't end
Message-ID:
<CAGRp5Rk0RwSe39n8zx+=tm61qrvwtzvgshps5fgwgft3lvk...@mail.gmail.com>
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How big are those lists? GHC will not be able to work out x+y+z < 50 will
never be true again, it will have to exhaustively consider *every*
combination.
On Sat, 23 Nov 2019, 6:38 pm Alexander Chen, <[email protected]> wrote:
> Hi,
>
> I am doing some further learning with euler now in Haskell instead of
> Julia. But I am getting something strange.
>
> [x+y+z | x <- a2, y <- b3, z <- c4, (x+y+z) < 50]
>
> a2, b3, c4 are all finite lists derived from the lazy list of the primes
> package. the output is:
>
> [28,47,33,49
>
> this is not a typo it is still calculating hence the missing bracket (for
> the last couple of hours, when to a christmas fair in between). The only
> thing is that, this should be the answer:
>
> [28,47,33,49]
>
>
> so it should be done but its not. what am I doing wrong?
>
> best,
>
>
>
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 3
Date: Sat, 23 Nov 2019 20:05:32 +0100
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] list doesn't end
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello Alexander,
On Sat, Nov 23, 2019 at 07:38:03PM +0100, Alexander Chen wrote:
> Hi,
>
> I am doing some further learning with euler now in Haskell instead of Julia.
> But I am getting something strange.
>
> [x+y+z | x <- a2, y <- b3, z <- c4, (x+y+z) < 50]
>
> a2, b3, c4 are all finite lists derived from the lazy list of the primes
> package. the output is:
>
> [28,47,33,49
λ> :m Data.Numbers.Primes
λ> let a = take 100 primes
λ> length [x+y+x | x <- a, y <- a, z <- a, (x+y+z) < 50]
942
I suspect one in [a2, b3, c4] is infinite (or very very long). Can you
paste the whole calculation?
-F
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