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Today's Topics:
1. question about any (Manfred Lotz)
2. Re: question about any (Tim Baumgartner)
3. Re: The numeric type stack (Brandon Allbery)
4. Re: question about any (Chadda? Fouch?)
5. Re: question about any (Markus L?ll)
----------------------------------------------------------------------
Message: 1
Date: Thu, 29 Dec 2011 06:45:27 +0100
From: Manfred Lotz <[email protected]>
Subject: [Haskell-beginners] question about any
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII
Hi there,
might be trivial but anyway.
I have a usage of 'any' and 'all' but I only have a predicate
p :: a -> IO Bool.
I wrote my own functons for this:
mor :: Monad m => [m Bool] -> m Bool
mor = liftM or . sequence
mand :: Monad m => [m Bool] -> m Bool
mand = liftM and . sequence
or' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
or' _ [] = []
or' p (x:xs) = p x : or' p xs
and' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
and' _ [] = []
and' p (x:xs) = p x : and' p xs
myany :: Monad m => (a -> m Bool) -> [a] -> m Bool
myany p = mor . or' p
myall :: Monad m => (a -> m Bool) -> [a] -> m Bool
myall p = mand . and' p
which seems to do what I want.
Question: Is there any libray function I could use to do this?
--
Thanks,
Manfred
------------------------------
Message: 2
Date: Thu, 29 Dec 2011 08:29:41 +0100
From: Tim Baumgartner <[email protected]>
Subject: Re: [Haskell-beginners] question about any
To: Manfred Lotz <[email protected]>
Cc: [email protected]
Message-ID:
<cae0z8dgf9n8gualzshbytbofngfcu_ukgpahdrcepdzbubh...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
2011/12/29 Manfred Lotz <[email protected]>
> Hi there,
> might be trivial but anyway.
>
> I have a usage of 'any' and 'all' but I only have a predicate
> p :: a -> IO Bool.
>
> I wrote my own functons for this:
>
>
> mor :: Monad m => [m Bool] -> m Bool
> mor = liftM or . sequence
>
> mand :: Monad m => [m Bool] -> m Bool
> mand = liftM and . sequence
>
> or' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
> or' _ [] = []
> or' p (x:xs) = p x : or' p xs
>
> and' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
> and' _ [] = []
> and' p (x:xs) = p x : and' p xs
>
> myany :: Monad m => (a -> m Bool) -> [a] -> m Bool
> myany p = mor . or' p
>
> myall :: Monad m => (a -> m Bool) -> [a] -> m Bool
> myall p = mand . and' p
>
>
> which seems to do what I want.
>
>
> Question: Is there any libray function I could use to do this?
>
>
> --
> Thanks,
> Manfred
>
Hi Manfred,
have a look here:
http://hackage.haskell.org/packages/archive/monad-loops/latest/doc/html/Control-Monad-Loops.html#v:allM
Regards Tim
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Message: 3
Date: Thu, 29 Dec 2011 04:49:53 -0500
From: Brandon Allbery <[email protected]>
Subject: Re: [Haskell-beginners] The numeric type stack
To: Mike Meyer <[email protected]>
Cc: beginners <[email protected]>
Message-ID:
<cakfcl4u9aj2ysvlq9yuebjjqyu8gmih3dbt2t3nq+3cx-ci...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Thu, Dec 29, 2011 at 00:33, Mike Meyer <[email protected]> wrote:
> So, is there a reasonable way to get the value of two Integral types
> divided by each other and rounded? How about one integral type and one
> RealFrac? I know I can get it truncated towards either 0 or negative
> infinity, but that's not what I want here.
>
You have two options:
(1) use fromIntegral to coerce an Integral value to a RealFrac;
(2) use (div) (division on Integrals) instead of (/).
Which to use depends on what you're planning to do with the result. In
this case, I'd probably use (/) and (fromIntegral).
--
brandon s allbery [email protected]
wandering unix systems administrator (available) (412) 475-9364 vm/sms
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------------------------------
Message: 4
Date: Thu, 29 Dec 2011 10:59:46 +0100
From: Chadda? Fouch? <[email protected]>
Subject: Re: [Haskell-beginners] question about any
To: Tim Baumgartner <[email protected]>
Cc: [email protected], Manfred Lotz <[email protected]>
Message-ID:
<CANfjZRZO6fyfDtJHHq_MbSiFy=jJH0z6r7RisgHdm+=zjxl...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Thu, Dec 29, 2011 at 8:29 AM, Tim Baumgartner
<[email protected]> wrote:
> 2011/12/29 Manfred Lotz <[email protected]>
>>
>> Hi there,
>> might be trivial but anyway.
>>
>> I have a usage of 'any' and 'all' but I only have a predicate
>> p :: a -> IO Bool.
>>
>> I wrote my own functons for this:
>>
>>
>> mor :: Monad m => [m Bool] -> m Bool
>> mor = liftM or . sequence
....
>> myall p = mand . and' p
>>
>
> Hi Manfred,
>
> have a look here:
> http://hackage.haskell.org/packages/archive/monad-loops/latest/doc/html/Control-Monad-Loops.html#v:allM
>
Note that your functions and those of Control.Monad.Loops don't do the
same thing : yours don't short circuit, they have to apply the
predicate to all the list elements, C.M.L gives you short-circuiting
combinators, that answer as soon as possible. You probably want C.M.L
behaviour for performance. (I'm lying a bit here, in fact in certain
monads (lazy ones), yours could be short-circuiting too, but in IO for
instance, that is not the case)
--
Jeda?
------------------------------
Message: 5
Date: Thu, 29 Dec 2011 12:14:30 +0200
From: Markus L?ll <[email protected]>
Subject: Re: [Haskell-beginners] question about any
To: Manfred Lotz <[email protected]>, [email protected]
Message-ID:
<caldaiuaa-3kq3nfgwte6gfgsgqcqronrapqajeuth7pdann...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
You can use 'mapM' similar to 'map', to get the resultant list in the
monad, and then liftM the function 'or' into it. This way you don't
need to recurse explicitly, like in or' and and'.
many :: Monad m => (a -> m Bool) -> [a] -> m Bool
many p list = or `liftM` mapM p list
(Type of mapM is: Monad m => (a -> m b) -> [a] -> m [b])
On Thu, Dec 29, 2011 at 7:45 AM, Manfred Lotz <[email protected]> wrote:
> Hi there,
> might be trivial but anyway.
>
> I have a usage of 'any' and 'all' but I only have a predicate
> p :: a -> IO Bool.
>
> I wrote my own functons for this:
>
>
> mor :: Monad m => [m Bool] -> m Bool
> mor = liftM or . sequence
>
> mand :: Monad m => [m Bool] -> m Bool
> mand = liftM and . sequence
>
> or' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
> or' _ [] = []
> or' p (x:xs) = p x : or' p xs
>
> and' :: Monad m => ( a -> m Bool) -> [a] -> [m Bool]
> and' _ [] = []
> and' p (x:xs) = p x : and' p xs
>
> myany :: Monad m => (a -> m Bool) -> [a] -> m Bool
> myany p = mor . or' p
>
> myall :: Monad m => (a -> m Bool) -> [a] -> m Bool
> myall p = mand . and' p
>
>
> which seems to do what I want.
>
>
> Question: Is there any libray function I could use to do this?
>
>
> --
> Thanks,
> Manfred
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
--
Markus L?ll
------------------------------
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