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Today's Topics:
1. Re: '/' instead use 'DIV'. why? (amin...@gmail.com)
2. Why the compiler does not commit to a type class?
(Alexander Chen)
3. Re: Why the compiler does not commit to a type class?
(Jason Chau)
----------------------------------------------------------------------
Message: 1
Date: Fri, 17 Apr 2020 15:42:46 -0400
From: amin...@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] '/' instead use 'DIV'. why?
Message-ID: <8a974ead-b22e-44e3-9974-ff16b19f7...@gmail.com>
Content-Type: text/plain; charset="utf-8"
It might help to imagine if you flip your arguments:
length [23, 34, 45] / 6 :: Int
How do you represent 3/6 as an Int?
> El 17 abr 2020, a las 03:19, Alexander Chen <alexan...@chenjia.nl> escribió:
>
> Hi,
>
>
> Prelude> :t (/)
> (/) :: Fractional a => a -> a -> a
>
> Prelude> :t div
> div :: Integral a => a -> a -> a
>
>
> Prelude> 6 / length [23,34,45]
> error
>
> Prelude> 6 / 3
> 2.0
>
> Could somebody explain to me why this is?
>
> thanks,
>
> Alexander Chen
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
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Message: 2
Date: Fri, 17 Apr 2020 21:56:16 +0200 (CEST)
From: Alexander Chen <alexan...@chenjia.nl>
To: beginners@haskell.org
Subject: [Haskell-beginners] Why the compiler does not commit to a
type class?
Message-ID: <1426914449.1477761.1587153376...@ichabod.co-bxl>
Content-Type: text/plain; charset="utf-8"
hi,
Prelude> u = undefined
Prelude> k :: (Ord a, Num b) => a -> b -> a; k = u
Prelude> :t k 1 2
k 1 2 :: (Ord a, Num a) => a
Prelude> :t k (1 :: Integer) 2
k (1 :: Integer) 2 :: Integer
In the first version the compiler is not really pushed so it simply gives back
the type class constriction it has to adhere to. While in the second it is
pushed to give an more specific answer and thus the :: Integer.
Question:
Is this train of thought correct?
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Message: 3
Date: Fri, 17 Apr 2020 13:00:28 -0700
From: Jason Chau <jasonsyc...@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 the compiler does not commit to a
type class?
Message-ID: <bac9641d-4eec-43db-8f22-734283bce...@gmail.com>
Content-Type: text/plain; charset="utf-8"
Yes - if you look at the number types, you will find different number types and
not integer types are providing support that’s not in Integer, so compiler is
giving safest assumption.
Sent from my iPhone
> On Apr 17, 2020, at 12:56 PM, Alexander Chen <alexan...@chenjia.nl> wrote:
>
>
> hi,
>
> Prelude> u = undefined
> Prelude> k :: (Ord a, Num b) => a -> b -> a; k = u
>
> Prelude> :t k 1 2
> k 1 2 :: (Ord a, Num a) => a
>
> Prelude> :t k (1 :: Integer) 2
> k (1 :: Integer) 2 :: Integer
>
> In the first version the compiler is not really pushed so it simply gives
> back the type class constriction it has to adhere to. While in the second it
> is pushed to give an more specific answer and thus the :: Integer.
>
> Question:
> Is this train of thought correct?
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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