How to fix Type matching error

Question

I am writing a function to calculate radius, and the first input is centre of a circle and second is a point from the edge of the circle.

type Coord = (Int,Int)
getRadius :: Coord -> Coord -> Float
getRadius (x0,y0) (x1,y1) = sqrt(sqrX+sqrY)
                             where sqrX = (x1-x0)*(x1-x0)
                                   sqrY = (y1-y0)*(y1-y0)

This is my code but when I compile it , an error shows that "Couldn't match expected type ‘Float’ with actual type ‘Int’. " I think the output should be a float not int . How can I fix this error? thanks

Frequently if one only needs to compare distances, one does not calculate the distance, but the square distance, so in such case, you could drop the sqrt. — Willem Van Onsem

Igor Drozdov Igor Drozdov · Accepted Answer · 2018-05-07T09:20:24

The problem is that sqrt accepts Floating number, but fromIntegral will help to explicitly type cast the integers to floating numbers:

getRadius :: Coord -> Coord -> Float
getRadius (x0,y0) (x1,y1) = sqrt(fromIntegral (sqrX+sqrY))
                             where sqrX = (x1-x0)*(x1-x0)
                                   sqrY = (y1-y0)*(y1-y0)

How to fix Type matching error

1 Answers