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Today's Topics:
1. List of a Data Type (Thomas Jakway)
2. Re: List of a Data Type (Alex Hammel)
3. Re: List of a Data Type (Ozgur Akgun)
4. Re: List of a Data Type (Thomas Jakway)
5. Add parenthesis to Sin/Cos expressions (goforgit .)
6. Re: Add parenthesis to Sin/Cos expressions (Imants Cekusins)
7. Re: randmomR produces only even values (Dominic Steinitz)
----------------------------------------------------------------------
Message: 1
Date: Tue, 3 Nov 2015 17:24:05 -0500
From: Thomas Jakway <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] List of a Data Type
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
I've made a new datatype
data Visibility a = Hidden a | Shown a
I want to create a type that's a list of hidden and visible integers.
So something like this:
type possiblyVisibleInts = [Visibility Int]
The idea is that some of the ints will be hidden and some will be shown.
But it doesn't work. Why not?
This seemed even odder to me after poking around in ghci:
:t [Just 5, Nothing]
gives
[Just 5, Nothing] :: Num a => [Maybe a]
So clearly it's possible to have a list of a type that has 2
constructors--you're not restricted to having a list that only contains
Just, for example.
ghci is also OK with e.g.
:t [Hidden 5, Shown 6]
[Hidden 5, Shown 6] :: Num a => [Visibility a]
------------------------------
Message: 2
Date: Tue, 03 Nov 2015 22:34:19 +0000
From: Alex Hammel <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] List of a Data Type
Message-ID:
<ca+_xfep2mgwjerqvxcaxejwtmpd20fhfy_2zr59fowmrmze...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Works for me:
Prelude> data Vis a = Hidden a | Shown a
Prelude> :t [Hidden "foo", Shown "bar"]
[Hidden "foo", Shown "bar"] :: [Vis [Char]]
Prelude> type VisListInt = [Vis Int]
Prelude> let foo = (id :: VisListInt -> VisListInt)
Prelude> :t foo
foo :: VisListInt -> VisListInt
Prelude> :t foo [Hidden 2]
foo [Hidden 2] :: VisListInt
What error message are you seeing?
Cheers,
Alex
On Tue, 3 Nov 2015 at 14:24 Thomas Jakway <[email protected]> wrote:
> I've made a new datatype
>
> data Visibility a = Hidden a | Shown a
>
> I want to create a type that's a list of hidden and visible integers.
> So something like this:
>
> type possiblyVisibleInts = [Visibility Int]
>
> The idea is that some of the ints will be hidden and some will be shown.
>
> But it doesn't work. Why not?
> This seemed even odder to me after poking around in ghci:
>
> :t [Just 5, Nothing]
> gives
> [Just 5, Nothing] :: Num a => [Maybe a]
>
> So clearly it's possible to have a list of a type that has 2
> constructors--you're not restricted to having a list that only contains
> Just, for example.
>
> ghci is also OK with e.g.
>
> :t [Hidden 5, Shown 6]
> [Hidden 5, Shown 6] :: Num a => [Visibility a]
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 3
Date: Tue, 3 Nov 2015 22:45:18 +0000
From: Ozgur Akgun <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] List of a Data Type
Message-ID:
<CALzazPC81-8oRXhCNtqVHmL53Vh1z=6b1mpywhbydrp0h_2...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On 3 November 2015 at 22:24, Thomas Jakway <[email protected]> wrote:
> type possiblyVisibleInts = [Visibility Int]
>
The case of the first letter is important: for type names, the first letter
has to be capital.
Ozgur
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Message: 4
Date: Tue, 3 Nov 2015 17:59:29 -0500
From: Thomas Jakway <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] List of a Data Type
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
Woops, thanks a ton!
On 11/3/15 5:45 PM, Ozgur Akgun wrote:
>
> On 3 November 2015 at 22:24, Thomas Jakway <[email protected]
> <mailto:[email protected]>> wrote:
>
> type possiblyVisibleInts = [Visibility Int]
>
>
> The case of the first letter is important: for type names, the first
> letter has to be capital.
>
> Ozgur
>
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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Message: 5
Date: Wed, 4 Nov 2015 08:29:24 +0100
From: "goforgit ." <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Add parenthesis to Sin/Cos expressions
Message-ID:
<CAHzzbMAzWoAqPim1bbqCE87bpV+vfgUxX0_a=1qbndnjhwd...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hello!
I've written a function that is supposed to add parenthesis to sin/cos
expressions.
For example
- Sin5+3 -> Sin(5) + 3
- SinCos(5+3) -> Sin(Cos(5+3))
- SinCos5 * 3 -> Sin(Cos(5)) * 3
The problem is that it converts the following expression
*SinSin(5+1+2)*
into
*Sin(Sin(5)+1+2)*
Could someone point me to the direction of a solution to this? Thanks in
advance!
convert :: String ->
String
convert s = convert' s
0
convert' :: String -> Int ->
String
convert' [] n =
replicate n ')'
convert' (a:as) n | ((a == 'n' || a == 's') && ((take 1 as) /= "(")) = a :
"(" ++ (convert' as (n+1))
| ((a == '+' || a == '*') && (n > 0)) =
(replicate n ')') ++ [a] ++ (convert' as 0)
| otherwise = a :
(convert' as n)
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Message: 6
Date: Wed, 4 Nov 2015 10:21:18 +0100
From: Imants Cekusins <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Add parenthesis to Sin/Cos
expressions
Message-ID:
<cap1qinyzbk6omziwuwy1ao+punq4qdogda79jwxz5jfipsp...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
> a function that is supposed to add parenthesis to sin/cos expressions.
a) Sin 5 + 3 -> Sin(5) + 3
b) Sin Cos (5+3) -> Sin (Cos(5+3))
c) Sin Cos 5 * 3 -> Sin(Cos(5)) * 3
are you looking for textual representation or actual Haskell code which runs?
if actual code, these examples may be re-written like this:
a) sin 5 + 3
b) sin $ cos $ 5 + 3
c) sin (cos 5) * 3
------------------------------
Message: 7
Date: Wed, 4 Nov 2015 09:58:15 +0000 (UTC)
From: Dominic Steinitz <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] randmomR produces only even values
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
> http://article.gmane.org/gmane.comp.lang.haskell.beginners/15925
I do think this is a flaw and catches many people out despite apparently
being well documented. And it's something one probably wants e.g. to run
multiple Markov Chain Monte Carlo simulations in parallel.
Some further information here:
https://github.com/haskell/random/issues/30#issuecomment-153647055
Dominic
------------------------------
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