I am using a Haskell compiler online and I would like to be able to read two values from the keyboard (from the input box) two numbers but it throws an error and I do not know how to correct it.
g::Float -> Float -> Float
g n u = 2 - (7/(5**n*u))
main :: IO ()
main = do
n <- getLine
u <- getLine
putStrLn (show (g (read n u :: (Float->Float->Float))))
The read function has the following signature:
read :: Read a => String -> a
You are trying to call it with two arguments of type String ( n and u ) instead of one only; you have to apply the read function separately to each data.
On the other hand, the type annotation that you provide ( :: (Float->Float->Float) ) is that of the function g , but once the arguments are passed to it, the type is simply Float . It is not necessary to specify the type for the results of read , since Haskell can infer it by the type of the function g .
g :: Float -> Float -> Float
g n u = 2 - (7/(5**n*u))
main :: IO ()
main = do
n <- getLine
u <- getLine
putStrLn (show (g (read n) (read u)))
I was able to get the exercise by also defining the data type in the values of the entry
g::Float -> Float -> Float
g n u = 2 - (7/(5**n*u))
main :: IO ()
main = do
n <- getLine
u <- getLine
putStrLn (show (g (read n :: Float)(read u :: Float)))