Re: [Haskell-beginners] Problems with lifting code

2 Oct 2016

      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  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  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?)?
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