[Haskell-cafe] Newbie "Instance Of Floating Int" Error

Cale Gibbard cgibbard at gmail.com
Fri Apr 28 02:08:43 EDT 2006

One thing to try:
type Point = (Float, Float)

The problem is that x1, y1, x2, and y2 are Ints, and so (x2-x1)^2  +
(y2-y1)^2 is also an Int, but then you try to take the square root,
which is an operation only available on floating point values (more
specifically, types in the class Floating, which also includes things
like Complex Double).

Another option is to leave the Point type as-is, but do a conversion
just before applying the sqrt, say, by applying the fromIntegral
function, which serves to convert from types in the class Integral,
like Int and Integer to any numeric type you need.
distBetween (x1,y1) (x2,y2) = sqrt . fromIntegral $ (x2-x1)^2 + (y2-y1)^2

hope this helps,
 - Cale

On 27/04/06, Aditya Siram <aditya_siram at hotmail.com> wrote:
> Hi all,
> I just started working with Haskell and am having some difficulties with its
> type system.
> Here is function that is supposed to calculate the distance between two
> coordinates:
> distBetween (x1,y1) (x2,y2) = sqrt((x2-x1)^2  + (y2-y1)^2)
> I am trying to explictly give it a type signature. Here is what I have tried
> and the errors generated by Hugs:
> type Point = (Int,Int)
> distBetween :: Point -> Point -> Float
> >>ERROR - Type error in explicitly typed binding
> *** Term           : distBetween
> *** Type           : Point -> Point -> Int
> *** Does not match : Point -> Point -> Float
> distBetween :: Point -> Point -> Int
> >>Instance of Floating Int required for definition of distBetween
> Any help is appreciated...
> Deech
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