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Int, Integer, Double

Haskell

Last updated at 2013-07-07Posted at 2013-06-30

Sometimes, ghc throws following error:

:7:21:
Couldn't match expected type Double' with actual type Int'
In the second argument of (/)', namely (3 :: Int)'
In the expression: (10.0 :: Double) / (3 :: Int)
In an equation for `it': it = (10.0 :: Double) / (3 :: Int)

(/) required to have the same type, which is Fractional type class.

Prelude> :t (/)
(/) :: Fractional a => a -> a -> a

Prelude> :i Int
data Int = GHC.Types.I# GHC.Prim.Int# 	-- Defined in `GHC.Types'
instance Bounded Int -- Defined in `GHC.Enum'
instance Enum Int -- Defined in `GHC.Enum'
instance Eq Int -- Defined in `GHC.Classes'
instance Integral Int -- Defined in `GHC.Real'
instance Num Int -- Defined in `GHC.Num'
instance Ord Int -- Defined in `GHC.Classes'
instance Read Int -- Defined in `GHC.Read'
instance Real Int -- Defined in `GHC.Real'
instance Show Int -- Defined in `GHC.Show'

fromIntegral helps to convert Integer or Int to Num.

Prelude> :t fromIntegral 
fromIntegral :: (Integral a, Num b) => a -> b

Still Num is not Fractional.

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