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Today's Topics:
1. why doesn't this work? (Alexander Chen)
2. Re: why doesn't this work? (Oliver Charles)
3. Re: why doesn't this work? (Ut Primum)
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Message: 1
Date: Wed, 8 Jan 2020 16:01:20 +0100 (CET)
From: Alexander Chen <alexan...@chenjia.nl>
To: beginners@haskell.org
Subject: [Haskell-beginners] why doesn't this work?
Message-ID: <675050120.318296.1578495680...@ichabod.co-bxl>
Content-Type: text/plain; charset="utf-8"
hi,
for a List comprehension I want to only include the integers of a division. In
my beginners mind this should work:
(round (x / y)) == (x / y)
however, i get a nontrivial error blurp.
what am i doing wrong?
best,
AlexanderÂ
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Message: 2
Date: Wed, 08 Jan 2020 16:37:47 +0000
From: "Oliver Charles" <ol...@ocharles.org.uk>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] why doesn't this work?
Message-ID: <ef1efd77-6d1c-4a07-94d5-d5125947d...@www.fastmail.com>
Content-Type: text/plain; charset="utf-8"
On Wed, 8 Jan 2020, at 3:01 PM, Alexander Chen wrote:
> hi,
>
> for a List comprehension I want to only include the integers of a division.
> In my beginners mind this should work:
>
> (round (x / y)) == (x / y)
>
> however, i get a nontrivial error blurp.
Could you share what the "nontrivial error blurp" is? It will be easier for
people to reply to you if they can see the problem without
having to reproduce it manually.
Ollie
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Message: 3
Date: Wed, 8 Jan 2020 18:50:35 +0100
From: Ut Primum <utpri...@gmail.com>
To: Alexander Chen <alexan...@chenjia.nl>, The Haskell-Beginners
Mailing List - Discussion of primarily beginner-level topics related
to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] why doesn't this work?
Message-ID:
<canjdmkjmrajergqere4cr0gmasqh2dnh36pw4hvw_ekdu3c...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I think the problem is in the types.
If you look at the type of the function round, you can see its result is an
Integral:
>> :t round
round :: (Integral b, RealFrac a) => a -> b
The result of the division x/y, instead, is a Fractional, and you cannot
test equality between two things of different types.
To solve the problem you can do a type cast, by converting the Integral to
a Num, using fromInteger:
(fromInteger (round (x/y))) == (x/y)
This should work.
Cheers,
Ut
Il giorno mer 8 gen 2020 alle ore 16:01 Alexander Chen <alexan...@chenjia.nl>
ha scritto:
> hi,
>
> for a List comprehension I want to only include the integers of a
> division. In my beginners mind this should work:
>
> (round (x / y)) == (x / y)
>
> however, i get a nontrivial error blurp.
>
> what am i doing wrong?
>
> best,
>
> Alexander
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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