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Today's Topics:
1. Mixed division (Lawrence Bottorff)
2. Re: Mixed division (Ut Primum)
3. Re: Mixed division (Lawrence Bottorff)
4. Cabal Build (A. Mc.)
5. Function with mod cases? (Lawrence Bottorff)
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Message: 1
Date: Fri, 5 Feb 2021 12:22:52 -0600
From: Lawrence Bottorff <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Mixed division
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<CAFAhFSWOpSxs1UK0B-xBSG+gnqECaGg3TU_WE-waShncm=u...@mail.gmail.com>
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I can divide a float by an integer
> 2.4 / 3
0.7999999999999999
but why can I not do this?
< 2.4 / (length [1,2,3])
<interactive>:288:1-22: error:
* No instance for (Fractional Int) arising from a use of `/'
* In the expression: 2.4 / (length [1, 2, 3])
LB
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Message: 2
Date: Fri, 5 Feb 2021 19:28:51 +0100
From: Ut Primum <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Mixed division
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Hi,
when you write 3 Haskell sees it as a "num" while the type of the length
[1,2,3] is "int". So 3 and length [1,2,3] have not the same type.
Il ven 5 feb 2021, 19:23 Lawrence Bottorff <[email protected]> ha scritto:
> I can divide a float by an integer
>
> > 2.4 / 3
> 0.7999999999999999
>
> but why can I not do this?
>
> < 2.4 / (length [1,2,3])
> <interactive>:288:1-22: error:
> * No instance for (Fractional Int) arising from a use of `/'
> * In the expression: 2.4 / (length [1, 2, 3])
>
> LB
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 3
Date: Fri, 5 Feb 2021 12:36:03 -0600
From: Lawrence Bottorff <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Mixed division
Message-ID:
<CAFAhFSUOLGkPD4at9vtvvO1=refdovwwrtvmtrpplu6fhd5...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
This works
myAvg :: [Float] -> Float
myAvg [] = 0.0
myAvg xs = (foldr (+) 0.0 xs) / (fromIntegral (length xs) :: Float)
but is there a simpler way to "cast" the value of (length xs)?
On Fri, Feb 5, 2021 at 12:29 PM Ut Primum <[email protected]> wrote:
> Hi,
> when you write 3 Haskell sees it as a "num" while the type of the length
> [1,2,3] is "int". So 3 and length [1,2,3] have not the same type.
>
> Il ven 5 feb 2021, 19:23 Lawrence Bottorff <[email protected]> ha scritto:
>
>> I can divide a float by an integer
>>
>> > 2.4 / 3
>> 0.7999999999999999
>>
>> but why can I not do this?
>>
>> < 2.4 / (length [1,2,3])
>> <interactive>:288:1-22: error:
>> * No instance for (Fractional Int) arising from a use of `/'
>> * In the expression: 2.4 / (length [1, 2, 3])
>>
>> LB
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 4
Date: Fri, 5 Feb 2021 16:42:52 -0800
From: "A. Mc." <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Cabal Build
Message-ID:
<CAOsti3=w41oErEdUSvNtGG=Adne9Hkb24M7c7j=neqnafyn...@mail.gmail.com>
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Hello,
I've been trying to do a cabal build. I'm using Windows 10. But, after
going through cabal init, change diretories, run, etc it keeps telling me I
don't have permission. My project also has 2 libraries that I wrote for
main, and although I tried editing the .cabal file, I'm not sure I have it
right.
Thanks in advance and thank you for your time.
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Message: 5
Date: Fri, 5 Feb 2021 22:18:31 -0600
From: Lawrence Bottorff <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Function with mod cases?
Message-ID:
<CAFAhFSV45uiiV7G_SaMTiBkq8fQL=UWKdi=7p4o1i8y+jgw...@mail.gmail.com>
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I'm looking through *An Introduction to Functional Programming Systems
Using Haskell *by Davie and one of the exercises is
*Define a function* f *such that*
f(x) = x + 3 (mod 5)
*Make a version that elaborates cases, as well as a straightforward way.*
I'm not really sure what's being asked, so this is what I've come up with
myMods xs = map (\x -> (x + 3) `mod` 5) xs
> myMods [1..20]
[4,0,1,2,3,4,0,1,2,3,4,0,1,2,3,4,0,1,2,3]
but when he says *make a version that elaborates cases *I'm not sure what
more there is to do.
What am I missing?
LB
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