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Today's Topics:

   1.  How long is the pointer from a Vector valid (after it has
      been extracted by unsafeWidth) (Nathan H?sken)
   2. Re:  How to convert a float or double number into a string?
      (Kim-Ee Yeoh)
   3.  question about pattern guards (TP)
   4. Re:  How to convert a float or double number into a string?
      (yi lu)
   5.  Inverse trig functions (Adrian May)
   6. Re:  Inverse trig functions (Martin Ruderer)
   7. Re:  Inverse trig functions (Adrian May)
   8. Re:  Inverse trig functions (Martin Ruderer)


----------------------------------------------------------------------

Message: 1
Date: Thu, 19 Sep 2013 14:26:57 +0200
From: Nathan H?sken <nathan.hues...@posteo.de>
To: beginners@haskell.org
Subject: [Haskell-beginners] How long is the pointer from a Vector
        valid (after it has been extracted by unsafeWidth)
Message-ID: <523aed91.9090...@posteo.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hey,

Background: I am making a wxhaskell backend for diagrams. Currently I am 
attempting to implement dashing. The function

penSetDashes :: Pen a -> Int -> Ptr c -> IO ()

takes a bit muster, represented by an array of chars (second parameter 
is the number of the used bits).
The problem is, that the underlying C++ function expects the pointer to 
be valid even after the function has been executed (until the pen is 
deleted or another dashing is set).

So I am creating a Vector Word8 with the desired bitmuster and I am 
using Data.Vector.Storable.withUnsafe to pass its internal pointer to 
penSetDashes.

But the pointer must point to something valid even after that!
So I was thinking, what if I define

data MyPen a = MyPen (Pen a) (Vector Word8)

and always keep the vector of dashes with the pen. Will the pointer stay 
valid?

If there are other Ideas on how to this, I am open!

Regards,
Nathan


------------------------------

Message: 2
Date: Thu, 19 Sep 2013 23:39:41 +0700
From: Kim-Ee Yeoh <k...@atamo.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
        beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] How to convert a float or double
        number into a string?
Message-ID:
        <capy+zdrds97btri4wrnlh_ko4lvu4hpvh3rsq0uvpemh5rx...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

On Wed, Sep 18, 2013 at 8:14 PM, yi lu <zhiwudazhanjiang...@gmail.com>wrote:

> What I need is just as much number of digits as possible. If I can hold as
> many digits of pi, i.e. 3.1415926535... as possible and save it in a
> String, it will be perfect!
>

Perhaps you had some experience with a computer algebra system (Maple,
Mathematica, etc.) and was expecting similar behavior?

While it's certainly possible to build it on top of Haskell, these kind of
floating-point features aren't available out of the box. Haskell provides
only fixed-bitwidth floating point.

As Oscar recommended, you probably want a String -> String function, say

> toEnglish "1.239402874"
"one point two three nine four zero blah blah"

-- Kim-Ee
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Message: 3
Date: Fri, 20 Sep 2013 00:20:45 +0200
From: TP <paratribulati...@free.fr>
To: beginners@haskell.org
Subject: [Haskell-beginners] question about pattern guards
Message-ID: <tu9sga-1mo.ln1@rama.universe>
Content-Type: text/plain; charset="ISO-8859-1"

Hi,

I have a question related to pattern guards in the syntax of Haskell 2010. 
Why is it not possible to combine them with a logical OR, instead of the 
comma that stands for a logical AND?

http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#pattern-guards

Thanks,

TP



------------------------------

Message: 4
Date: Fri, 20 Sep 2013 08:44:50 +0800
From: yi lu <zhiwudazhanjiang...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
        beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] How to convert a float or double
        number into a string?
Message-ID:
        <cakcmqqxy1nz-+x7ezpnxejbpzumcq-ahqlpnivy7gk0a1x-...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Thank you all! I am considering defining a String -> String function now.


On Fri, Sep 20, 2013 at 12:39 AM, Kim-Ee Yeoh <k...@atamo.com> wrote:

>
> On Wed, Sep 18, 2013 at 8:14 PM, yi lu <zhiwudazhanjiang...@gmail.com>wrote:
>
>> What I need is just as much number of digits as possible. If I can hold
>> as many digits of pi, i.e. 3.1415926535... as possible and save it in a
>> String, it will be perfect!
>>
>
> Perhaps you had some experience with a computer algebra system (Maple,
> Mathematica, etc.) and was expecting similar behavior?
>
> While it's certainly possible to build it on top of Haskell, these kind of
> floating-point features aren't available out of the box. Haskell provides
> only fixed-bitwidth floating point.
>
> As Oscar recommended, you probably want a String -> String function, say
>
> > toEnglish "1.239402874"
> "one point two three nine four zero blah blah"
>
> -- Kim-Ee
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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Message: 5
Date: Fri, 20 Sep 2013 18:11:42 +0800
From: Adrian May <adrian.alexander....@gmail.com>
To: "beginners@haskell.org" <beginners@haskell.org>
Subject: [Haskell-beginners] Inverse trig functions
Message-ID:
        <cad-ubzhk9xtm-mtvp_awkq+arp2knlek93tfrtyvbr0joxv...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi All,

When Haskell says "inverse trig function", it seems to mean the inverse of
the return value of a trig function.

I want those functions that return an angle whose sine, cosine or whatever
equals the parameter I pass. Where are those?

TIA,
Adrian.
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Message: 6
Date: Fri, 20 Sep 2013 13:40:00 +0200
From: Martin Ruderer <martin.rude...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
        beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Inverse trig functions
Message-ID:
        <ca+t_wnajeuvvl9xytfrnd9yr6h9fhqw9xkvmitgkiy-wdu7...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Hello Adrian,

those would be called asin and acos.

Best regards,
Martin
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Message: 7
Date: Fri, 20 Sep 2013 19:52:34 +0800
From: Adrian May <adrian.alexander....@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
        beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Inverse trig functions
Message-ID:
        <cad-ubzgvv6b1kh+-okprlwqxwfo7ax1iv+y1vzfmdtyyrxa...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Apparently not. Those are 1/sin and 1/cos. I want to supply a ratio and get
an angle.


On 20 September 2013 19:40, Martin Ruderer <martin.rude...@gmail.com> wrote:

> Hello Adrian,
>
> those would be called asin and acos.
>
> Best regards,
> Martin
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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Message: 8
Date: Fri, 20 Sep 2013 13:59:50 +0200
From: Martin Ruderer <martin.rude...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
        beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Inverse trig functions
Message-ID:
        <CA+t_wNBjMZaoHpRsWBrgVUH8hoi+VYMra=qyjuc8m88wttw...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Are you sure?

Prelude> map (sin.asin) [0.1,0.3,0.5,0.7,0.9]
[0.1,0.3,0.5,0.7,0.9]



On Fri, Sep 20, 2013 at 1:52 PM, Adrian May
<adrian.alexander....@gmail.com>wrote:

> Apparently not. Those are 1/sin and 1/cos. I want to supply a ratio and
> get an angle.
>
>
> On 20 September 2013 19:40, Martin Ruderer <martin.rude...@gmail.com>wrote:
>
>> Hello Adrian,
>>
>> those would be called asin and acos.
>>
>> Best regards,
>> Martin
>>
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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