# Lifting to the limit

**Saswat Anand
**
iscp9157@nus.edu.sg

*Sat, 17 Feb 2001 10:50:19 -0800*

Thanks a lot. It works fine.
Could you help me with this. With the following defintions, I want to be
able to write
(high \+ 4) (3.4,2) and
(4 \+ high) (3.4,2) which both should be equal to 4+ (high 2) = 6.
But hugs gives following error during run time:
ERROR: Unresolved overloading
*** Type : Lift a => Integer
*** Expression : (high \+ 4) (1,1)
type Formula a b = a -> b
(\+) :: (Lift a,Lift c,Num b)=>Formula a b -> Formula c b -> Formula Env b
p \+ q = \env -> (lift p) env + (lift q) env
type Env = (Double,Integer)
class Lift a where
lift :: Formula a b -> Formula Env b
instance Lift Double where
lift f (c,i) = f c
instance Lift Integer where
lift f (c,i) = f i
instance Lift Env where
lift = id
high :: Formula Integer Integer
high n = n+1
low :: Formula Double Integer
low = round
instance Eq (Formula a b) where
(==) = error "<< error >>"
instance Show (Formula a b) where
showsPrec n a1 = error "<< Formula >>"
instance (Num b) => Num (Formula a b) where -- I tried instance (Lift a,
Num b) =>...... does not work
fromInteger x = \a -> fromInteger x
Thanks,
Saswat
----- Original Message -----
From: Ken Shan <ken@digitas.harvard.edu>
To: Saswat Anand <iscp9157@nus.edu.sg>
Cc: <haskell@haskell.org>
Sent: Friday, February 16, 2001 12:17 PM
Subject: Re: Lifting to the limit
>* Tis the season for type class overloading fun...
*>*
*>* On 2001-02-16T21:45:32+0800, Saswat Anand wrote:
*>* > lift2 :: (a -> b -> c) -> Formula d a -> Formula e b -> Formula Env c
*>*
*>* This type is too general. You need to specify a context that requires
*>* both d and e to satisfy Lift:
*>*
*>* lift2 :: (Lift d, Lift e) =>
*>* (a -> b -> c) -> Formula d a -> Formula e b -> Formula Env c
*>*
*>* --
*>* Edit this signature at
*>* http://rodimus.digitas.harvard.edu/cgi-bin/ken/sig
*>* "The day Microsoft makes something that doesn't suck is probably the day
*>* they start making vacuum cleaners" - Ernst Jan Plugge
*