gistfile1.hs

import System

class Hi a where
  hi :: a -> String

data Ujihisa = Ujihisa
instance Hi Ujihisa where
  hi = "my name is ujihisa"

data Ujm = Ujm
instance Hi Ujm where
  hi = "this is a pen"

main = do x <- getArgs
          let the_klass = if length x == 1 then Ujihisa else Ujm
          print $ hi the_klass



/var/folders/Dz/Dz5WpFSZGUaFLA8jp8kT5E+++TM/-Tmp-/vv6A9jF/341:4:61:
    Couldn't match expected type `Ujihisa' against inferred type `Ujm'
    In the expression: Ujm
    In the expression: if length x == 1 then Ujihisa else Ujm
    In the definition of `the_klass':
        the_klass = if length x == 1 then Ujihisa else Ujm

/var/folders/Dz/Dz5WpFSZGUaFLA8jp8kT5E+++TM/-Tmp-/vv6A9jF/341:12:7:
    Couldn't match expected type `Ujihisa -> String'
           against inferred type `[Char]'
    In the expression: "my name is ujihisa"
    In the definition of `hi': hi = "my name is ujihisa"
    In the instance declaration for `Hi Ujihisa'

/var/folders/Dz/Dz5WpFSZGUaFLA8jp8kT5E+++TM/-Tmp-/vv6A9jF/341:16:7:
    Couldn't match expected type `Ujm -> String'
           against inferred type `[Char]'
    In the expression: "this is a pen"
    In the definition of `hi': hi = "this is a pen"
    In the instance declaration for `Hi Ujm'