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Today's Topics:
1. Problems with lifting code (PATRICK BROWNE)
2. Re: Problems with lifting code (Francesco Ariis)
3. Re: Problems with lifting code (Imants Cekusins)
4. Re: Problems with lifting code (PATRICK BROWNE)
5. Re: Problems with lifting code (PATRICK BROWNE)
----------------------------------------------------------------------
Message: 1
Date: Sun, 2 Oct 2016 15:54:07 +0100
From: PATRICK BROWNE <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Problems with lifting code
Message-ID:
<cagflrkd+_+thpvmbkt65q93ok_ytigwkaxe1sg3ycibyv3q...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I am trying, without sucess, to run the code below from [1] (Section 4.3).
Obviouly I am missing something.
I would like to keep as close to the original code as possible.
Any help would be apreciated.
Regards,
Pat
[1] http://publik.tuwien.ac.at/files/pub-geo_2321.pdf
data MyNumbers a = MyNum a deriving Show
class (Floating a) => Numbers a where
sqr :: a -> a
-- Not sure if i need these
-- instance Num (MyNumbers a) where
-- instance Fractional (MyNumbers a) where
class Lifts b a where
lift0 :: a -> b a
lift1 :: (a -> a) -> b a -> b a
instance Lifts MyNumbers a where
lift0 x = MyNum x
lift1 o x = MyNum (o x) -- ** Couldn't match expected type `a' with
actual type `MyNumbers a' **
instance (Floating (MyNumbers Float)) => Numbers (MyNumbers Float) where
sqr x = lift1 sqr x -- ** could not deduce (Numbers Float) arising from
a use of `sqr' **
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Message: 2
Date: Sun, 2 Oct 2016 17:38:24 +0200
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Problems with lifting code
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Sun, Oct 02, 2016 at 03:54:07PM +0100, PATRICK BROWNE wrote:
> Hi,
> I am trying, without sucess, to run the code below from [1] (Section 4.3).
> Obviouly I am missing something.
> I would like to keep as close to the original code as possible.
> Any help would be apreciated.
> Regards,
> Pat
> [1] http://publik.tuwien.ac.at/files/pub-geo_2321.pdf
>
I get different errors from yours (missing extension, Illegal
instance declaration). Can you paste the exact file you are
loading with ghci (because you are using ghci, right?)?
------------------------------
Message: 3
Date: Sun, 2 Oct 2016 17:57:54 +0200
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] Problems with lifting code
Message-ID:
<CAP1qinatCSeEbtKDjpZ9EnXW9R=m-utb9bgznx0p3+9mhos...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
this works:
{-# LANGUAGE MultiParamTypeClasses,FlexibleInstances #-}
module Lift where
newtype MyNumbers a = MyNum a deriving Show
class Numbers a where
sqr :: a -> a
class Lifts b a where
lift0 :: a -> b a
lift1 :: (a -> a) -> b a -> b a
instance Lifts MyNumbers a where
lift0 x = MyNum x
lift1 o (MyNum x) = MyNum (o x)
instance Numbers Float where
sqr x = x * x
instance Numbers (MyNumbers Float) where
sqr x = lift1 sqr x
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Message: 4
Date: Sun, 2 Oct 2016 17:03:25 +0100
From: PATRICK BROWNE <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Problems with lifting code
Message-ID:
<CAGFLrKd=kpajxsw7xkfakrzpqjzh3qnvotm7zzx9dvxtdoq...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Yes, I am running ghci 8.0.1.
Below, I have added the language pragmas suggested by the compiler
Regards,
Pat
.
{-# LANGUAGE
MultiParamTypeClasses,FlexibleInstances,FlexibleContexts,UndecidableInstances
#-}
data MyNumbers a = MyNum a deriving Show
class (Floating a) => Numbers a where
sqr :: a -> a
class Lifts b a where
lift0 :: a -> b a
lift1 :: (a -> a) -> b a -> b a
instance Lifts MyNumbers a where
lift0 x = MyNum x
lift1 o x = MyNum (o x)
instance (Floating (MyNumbers Float)) => Numbers (MyNumbers Float) where
sqr x = lift1 sqr x
On 2 October 2016 at 16:38, Francesco Ariis <[email protected]> wrote:
> On Sun, Oct 02, 2016 at 03:54:07PM +0100, PATRICK BROWNE wrote:
> > Hi,
> > I am trying, without sucess, to run the code below from [1] (Section
> 4.3).
> > Obviouly I am missing something.
> > I would like to keep as close to the original code as possible.
> > Any help would be apreciated.
> > Regards,
> > Pat
> > [1] http://publik.tuwien.ac.at/files/pub-geo_2321.pdf
> >
>
> I get different errors from yours (missing extension, Illegal
> instance declaration). Can you paste the exact file you are
> loading with ghci (because you are using ghci, right?)?
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 5
Date: Sun, 2 Oct 2016 17:15:57 +0100
From: PATRICK BROWNE <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Problems with lifting code
Message-ID:
<CAGFLrKdZ8C=k+frtbcrc6wupwag0hhcee9xlam9xu7v05wo...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
So it seems that
(1) lift1 o x = MyNum (o x)
Needed to be rewritten to
(2) lift1 o (MyNum x) = MyNum (o x)
I am not sure why the constructor is used on the LHS of (2)
Thanks for all your help.
Pat
On 2 October 2016 at 17:03, PATRICK BROWNE <[email protected]> wrote:
> Yes, I am running ghci 8.0.1.
> Below, I have added the language pragmas suggested by the compiler
> Regards,
> Pat
> .
> {-# LANGUAGE
> MultiParamTypeClasses,FlexibleInstances,FlexibleContexts,UndecidableInstances
> #-}
>
> data MyNumbers a = MyNum a deriving Show
>
> class (Floating a) => Numbers a where
> sqr :: a -> a
>
>
> class Lifts b a where
> lift0 :: a -> b a
> lift1 :: (a -> a) -> b a -> b a
>
> instance Lifts MyNumbers a where
> lift0 x = MyNum x
> lift1 o x = MyNum (o x)
>
> instance (Floating (MyNumbers Float)) => Numbers (MyNumbers Float) where
> sqr x = lift1 sqr x
>
> On 2 October 2016 at 16:38, Francesco Ariis <[email protected]> wrote:
>
>> On Sun, Oct 02, 2016 at 03:54:07PM +0100, PATRICK BROWNE wrote:
>> > Hi,
>> > I am trying, without sucess, to run the code below from [1] (Section
>> 4.3).
>> > Obviouly I am missing something.
>> > I would like to keep as close to the original code as possible.
>> > Any help would be apreciated.
>> > Regards,
>> > Pat
>> > [1] http://publik.tuwien.ac.at/files/pub-geo_2321.pdf
>> >
>>
>> I get different errors from yours (missing extension, Illegal
>> instance declaration). Can you paste the exact file you are
>> loading with ghci (because you are using ghci, right?)?
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>
>
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