相关疑难解决方法(0)

来自ghci：

Prelude> :i Num                              
class Num a where                            
  (+) :: a -> a -> a                         
  (-) :: a -> a -> a                         
  (*) :: a -> a -> a                         
  negate :: a -> a                           
  abs :: a -> a                              
  signum :: a -> a                           
  fromInteger :: Integer -> a                
        -- Defined in `GHC.Num'              
instance Num Word -- Defined in `GHC.Num'    
instance Num Integer -- Defined in `GHC.Num' 
instance Num Int -- Defined in `GHC.Num'     
instance Num Float -- Defined in …