[Haskell-cafe] Newbie Q: Deriving MyOrd from Eq problem

25 Jul 2006

      I am trying to derive MyOrd class from Eq (Prelude):

class Eq a => MyOrd a where
        (%<=), (%>), (%>=) :: a -> a -> Bool
        x %<= y = (x < y || x == y)
        x %> y =  y < x
        x %>= y = (y < x || x == y)

I get these errors:

ClassTest.hs:28:21:
    Could not deduce (Ord a) from the context (MyOrd a)
      arising from use of `<' at C:/wks/haskell-wks/ClassTest.hs:28:21
    Probable fix: add (Ord a) to the class or instance method `%<='
    In the first argument of `(||)', namely `x < y'
    In the definition of `%<=': %<= x y = ((x < y) || (x == y))
    In the definition for method `%<='

ClassTest.hs:29:20:
    Could not deduce (Ord a) from the context (MyOrd a)
      arising from use of `<' at C:/wks/haskell-wks/ClassTest.hs:29:20
    Probable fix: add (Ord a) to the class or instance method `%>'
    In the definition of `%>': %> x y = y < x
    In the definition for method `%>'

ClassTest.hs:30:21:
    Could not deduce (Ord a) from the context (MyOrd a)
      arising from use of `<' at C:/wks/haskell-wks/ClassTest.hs:30:21
    Probable fix: add (Ord a) to the class or instance method `%>='
    In the first argument of `(||)', namely `y < x'
    In the definition of `%>=': %>= x y = ((y < x) || (x == y))
    In the definition for method `%>='
Failed, modules loaded: none.

Q: What's wrong?  Why 'Ord' gets into play here?

Thanks,
Dima

[Haskell-cafe] Newbie Q: Deriving MyOrd from Eq problem

Dmitri O.Kondratiev