Thanks for the information. Michael --- On Mon, 3/30/09, Ryan Ingram wrote: From: Ryan Ingram Subject: Re: [Haskell-cafe] Rational and % operator remix To: "michael rice" Cc: "Ketil Malde" , haskell-cafe@haskell.org Date: Monday, March 30, 2009, 1:21 PM 2009/3/30 michael rice :

I'm still not sure what some of the error messages I was getting were about. As I wrote the function I tried to be aware of what "mixed mode" operations were kosher ala

This is a mistake, but understandable given your lispy background; there aren't really "mixed mode" operations in Haskell. One thing that might be confusing you: Numeric literals are really calls to "fromInteger"; that is, "5" is really "fromInteger (5 :: Integer)" Generally you will find that :t in the interpreter is your friend: ghci> :t 1 1 :: (Num t) => t This says that the expression "1" can be of any type that is an instance of Num. ghci> :t (\a b -> a - b) (\a b -> a - b) :: (Num a) => a -> a -> a "-" takes two arguments that are of the same type, and returns something of that type. ghci> :m Data.Ratio ghci> :t (%) (%) :: (Integral a) => a -> a -> Ratio a "%" lifts objects from an integral type into a type that represents the ratio of two integers. ghci> :t floor floor :: (RealFrac a, Integral b) :: a -> b So "floor" is a "cast" operation that converts between any fractional type to any integral type. This is why you need to either use "fromInteger" or "%" on the result of "floor" to get it back as a Rational.   -- ryan