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Today's Topics:
1. How to convert a float or double number into a string? (yi lu)
2. Re: Help getting glib installed (Britt Anderson)
3. Re: How to convert a float or double number into a string?
(Oscar Benjamin)
4. Re: How to convert a float or double number into a string?
(yi lu)
5. using the joker "_" on a constructor (TP)
6. Re: using the joker "_" on a constructor (Kim-Ee Yeoh)
7. Re: using the joker "_" on a constructor (David McBride)
8. Re: How to convert a float or double number into a string?
(Oscar Benjamin)
----------------------------------------------------------------------
Message: 1
Date: Wed, 18 Sep 2013 20:48:57 +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: [Haskell-beginners] How to convert a float or double number
into a string?
Message-ID:
<cakcmqqzr6ymxgvrhg6wexe0otxfj2ols5rje3c4s8s1b0t4...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
If I use `show`,
show 123.45, it will return "123.45", a desired answer.
However, for
show 123.45678901234567890, it will return
"123.45678901234568".
I want to save all digits into a string. I suppose I use a wrong type of
number, which is Float.
But what can I do to work right?
Yi
PS: If you receive this mail twice, please ignore one of them.
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Message: 2
Date: Wed, 18 Sep 2013 08:50:20 -0400
From: Britt Anderson <britt.ander...@uwaterloo.ca>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Help getting glib installed
Message-ID: <87wqmemgz7....@brittoffice.uwaterloo.ca>
Content-Type: text/plain
This suggestion worked well. glib installation problem [solved].
gte...@gmail.com writes:
> Cabal-1.18 was released very recently and packages that have custom build
> scripts are quite likely to be broken with it.
> If you dont need any features that this version brings you should be good
> with installing cabal-install-1.16.0.2 instead.
>
------------------------------
Message: 3
Date: Wed, 18 Sep 2013 14:00:59 +0100
From: Oscar Benjamin <oscar.j.benja...@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:
<CAHVvXxRa-scNMkY=-q5jdin+ng+1xr6edpeidycqtrgcofn...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On 18 September 2013 13:48, yi lu <zhiwudazhanjiang...@gmail.com> wrote:
> If I use `show`,
> show 123.45, it will return "123.45", a desired answer.
>
> However, for
> show 123.45678901234567890, it will return
> "123.45678901234568".
>
> I want to save all digits into a string. I suppose I use a wrong type of
> number, which is Float.
Yes, it is the wrong type of number. Float can only store finitely
many digits and you're asking for slightly too many. Also even if it
*looks like* float has enough digits for your number in fact it has
converted them from decimal to binary. For non-integers exact decimal
to binary conversion is rarely possible. In this case the nearest
binary float is 123.4567890123456805895330035127699375152587890625 but
many of these decimal digits will be truncated from display.
> But what can I do to work right?
Are rational numbers acceptable in your problem?
http://stackoverflow.com/questions/7056791/how-to-parse-a-decimal-fraction-into-rational-in-haskell
Oscar
------------------------------
Message: 4
Date: Wed, 18 Sep 2013 21:14:35 +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:
<CAKcmqqz5y8jahMvd3xGLcQPOawDy5gkqTWcV80La=a6obeo...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
In fact, I am not looking for some way to convert a float 0.75 to 3%4. Your
reply is helpful!
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!
Yi
On Wed, Sep 18, 2013 at 9:00 PM, Oscar Benjamin
<oscar.j.benja...@gmail.com>wrote:
> On 18 September 2013 13:48, yi lu <zhiwudazhanjiang...@gmail.com> wrote:
> > If I use `show`,
> > show 123.45, it will return "123.45", a desired answer.
> >
> > However, for
> > show 123.45678901234567890, it will return
> > "123.45678901234568".
> >
> > I want to save all digits into a string. I suppose I use a wrong type of
> > number, which is Float.
>
> Yes, it is the wrong type of number. Float can only store finitely
> many digits and you're asking for slightly too many. Also even if it
> *looks like* float has enough digits for your number in fact it has
> converted them from decimal to binary. For non-integers exact decimal
> to binary conversion is rarely possible. In this case the nearest
> binary float is 123.4567890123456805895330035127699375152587890625 but
> many of these decimal digits will be truncated from display.
>
> > But what can I do to work right?
>
> Are rational numbers acceptable in your problem?
>
> http://stackoverflow.com/questions/7056791/how-to-parse-a-decimal-fraction-into-rational-in-haskell
>
>
> Oscar
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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Message: 5
Date: Wed, 18 Sep 2013 16:08:24 +0200
From: TP <paratribulati...@free.fr>
To: beginners@haskell.org
Subject: [Haskell-beginners] using the joker "_" on a constructor
Message-ID: <onooga-c4g.ln1@rama.universe>
Content-Type: text/plain; charset="ISO-8859-1"
Hi,
I have a question about pattern matching.
Consider the following code:
------------------
data Foo = Bar Int
| Foo Int
f :: Foo -> Bool
f (Foo n)
| even n = True
| odd n = False
f (Bar n)
| even n = True
| odd n = False
main = do
print $ f $ Bar 1
print $ f $ Bar 2
print $ f $ Foo 1
print $ f $ Foo 2
------------------
Why is it not possible to simply write for f:
f v = case v of
_ n | even n -> True
_ n | odd n -> False
or
f (_ n)
| even n = True
| odd n = False
(in both cases we get a parse error)?
Thanks,
TP
------------------------------
Message: 6
Date: Wed, 18 Sep 2013 21:21:47 +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] using the joker "_" on a constructor
Message-ID:
<capy+zdrnauytu0g8_escs6y-pmyxugj1jqnf0jurvycnszc...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
On Wed, Sep 18, 2013 at 9:08 PM, TP <paratribulati...@free.fr> wrote:
> f :: Foo -> Bool
> f (Foo n)
> | even n = True
> | odd n = False
> f (Bar n)
> | even n = True
> | odd n = False
>
(1) Since even is monomorphized to Int -> Bool, you can just write
f (Foo n) = even n
f (Bar n) = even n
(2) Since the sum subtypes are the same, you can write
data Foo = Foo {myN :: Int} | Bar {myN :: Int}
f :: Foo -> Bool
f x = even $ myN x
(3) As to your original question why the underscore _ can't be overloaded
for this, I dunno. It /may/ be possible. Seems rare in practice. You could
always apply the type isomorphism to get
data FooT = Foo | Bar
data Foo = Foo Int FooT
f (Foo n _) = even n
-- Kim-Ee
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Message: 7
Date: Wed, 18 Sep 2013 10:22:27 -0400
From: David McBride <toa...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] using the joker "_" on a constructor
Message-ID:
<CAN+Tr423fsaNvE+vZE9oyJ7wPzENsP=6f8dtw0z8t2+24jg...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
It has to know the constructor in order to know the type of n. In your
case they are both int, but in the general case they could be completely
different types and therefore you could not just use the constructors
interchangeably.
If you want to write this I would go:
data Foo = Bar Int | Foo Int
def unFoo (Bar n) = n
def unFoo (Foo n) = n
f v = if even (unFoo n) then True else False
You could also define the data type as
data Foo = Bar { unFoo :: Int } | Foo { unFoo :: Int }
As long as you make sure unFoo works for every possibility (otherwise it
would be a partial function that could throw an exception).
On Wed, Sep 18, 2013 at 10:08 AM, TP <paratribulati...@free.fr> wrote:
> Hi,
>
> I have a question about pattern matching.
> Consider the following code:
>
> ------------------
> data Foo = Bar Int
> | Foo Int
>
> f :: Foo -> Bool
> f (Foo n)
> | even n = True
> | odd n = False
> f (Bar n)
> | even n = True
> | odd n = False
>
> main = do
>
> print $ f $ Bar 1
> print $ f $ Bar 2
> print $ f $ Foo 1
> print $ f $ Foo 2
> ------------------
>
> Why is it not possible to simply write for f:
>
> f v = case v of
> _ n | even n -> True
> _ n | odd n -> False
>
> or
>
> f (_ n)
> | even n = True
> | odd n = False
>
> (in both cases we get a parse error)?
>
> Thanks,
>
> TP
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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Message: 8
Date: Wed, 18 Sep 2013 15:23:48 +0100
From: Oscar Benjamin <oscar.j.benja...@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:
<cahvvxxsubgwdu-vedg9jt+z6jtl5f65ck5cxnckw1ny9q_a...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
On Sep 18, 2013 2:15 PM, "yi lu" <zhiwudazhanjiang...@gmail.com> wrote:
>
> In fact, I am not looking for some way to convert a float 0.75 to 3%4.
Your reply is helpful!
> 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!
I think something is still missing from your description.
If you want to store the digits of pi in a string then why not use a string?
Oscar
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