Конструирование типов данных

data Ordering = LT | EQ | GT

data LogLevel = Error | Warning | Info

cmp :: LogLevel -> LogLevel -> Ordering 
cmp = undefined

data Ordering = LT | EQ | GT
data LogLevel = Error | Warning | Info
 
class LogLevel a where
    cmp :: a -> a -> Ordering 
    cmp x y = if x = y then Warning else if x<=y then Info else Error

data LogLevel = Error | Warning | Info
        deriving (Eq,Ord)
 
cmp :: LogLevel -> LogLevel -> Ordering
cmp = compare
 
main =  print $ [cmp Error Warning, cmp Info Error]

data LogLevel = Error | Warning | Info
          deriving Show  
--        deriving (Eq,Ord)
 
cmp :: LogLevel -> LogLevel -> Ordering
cmp Error Error = EQ
cmp Warning Warning = EQ
cmp Info Info = EQ
cmp Error _ = LT
cmp Info _ = GT 
cmp _ Error = GT
cmp _ Info = LT 
 
main =  print $ [(x,y,cmp x y)| x <- diap, y <- diap]
    where diap = [Error,Warning,Info] -- если без всяких deriving, ну кроме Show, хотя и без него можно

cmp = undefined

cmp :: LogLevel -> LogLevel -> Ordering 
cmp x y
    | x == y = EQ
    | x == Info = LT
    | x == Error = GT
    | y == Info = GT
    | otherwise = LT

data LogLevel = Error | Warning | Info
          deriving (Show,Eq,Ord,Enum)
 
cmp :: LogLevel -> LogLevel -> Ordering
cmp = flip compare
 
main =  print $ [(x,y,cmp x y)| x <- diap, y <- diap]
    where diap = [Error .. Info]

import Data.List 
 
showOrd LT = "<" 
showOrd GT = ">"
showOrd _  = "="
 
data LogLevel = Error | Warning | Info
          deriving (Show,Eq,Ord,Enum)
 
cmp :: LogLevel -> LogLevel -> Ordering
cmp = flip compare
 
main =  mapM_ (\(x,y) -> putStrLn $ intercalate "\t" 
                 [show x, showOrd $ cmp x y, show y])
--              [(x,y)| x <- diap, y <- diap]
              $ do 
                 x <- diap
                 y <- diap
                 return (x,y)
    where diap = [Error .. Info]