Re: [Haskell-cafe] Question about classes from a Haskell newbie.

23 May 2005


      On 5/23/05, Jeff.Harper@handheld.com  wrote:
...
Hi,
I'm new to Haskell and even newer to this list.   I have over 20 years of
experience in C or C++.
For fun, I decided to write a Fourier transform in Haskell.  It would be
convenient if I had a function that converts any real or complex number into
a complex number.  My attempt at doing this is below.  Hugs produces errors
when I try to load this code.
Essentially, I'm trying to define a class called ConvertibleToComplex. 
There is a function in this class called toComplex.  toComplex has the type:
class ConvertibleToComplex a where 
   toComplex :: RealFloat b => a -> Complex b
I don't think you want an arbitrary type 'b'. Try: (pass -98 to Hugs
or -fglasgow-exts to GHCi when loading this code)

import Complex

class ConvertibleToComplex a b | a -> b where
   toComplex :: RealFloat b => a -> Complex b

instance ConvertibleToComplex Float Float where
        toComplex f = f :+ 0

instance ConvertibleToComplex Double Double where
        toComplex d = d :+ 0

instance ConvertibleToComplex (Complex a) a where
        toComplex c = c

-- 
Friendly,
  Lemmih