[Haskell-cafe] classes question
jfredett at gmail.com
Mon Nov 9 13:48:22 EST 2009
(+) is a name that is already taken by the Num typeclass, you're
trying to overload it with a different class. It's equivalent to doing:
foo :: Int
foo = 1
foo :: String
foo = "abc"
this would cause an (obvious) namespace collision. If you want to
redefine (+), you'll have to import a qualified prelude, by using the
pragma and `import qualified Prelude`.
A better alternative is to use a different name, `+`, `++` are both
taken (for normal addition and list concatenation, resp.).
On Nov 9, 2009, at 1:44 PM, Paul Tokarev wrote:
> I am using Hugs 98
> I have that piece of code:
> class PlusTimes a where
> plus :: a -> a -> a
> instance PlusTimes Int where
> plus x y = x + y
> when I run : "plus 2 3" I get this error:
> ERROR - Unresolved overloading
> *** Type : (Num a, PlusTimes a) => a
> *** Expression : plus 2 3
> What am I doing wrong?
> View this message in context: http://old.nabble.com/classes-question-tp26271257p26271257.html
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