-- Adapted from Data Field Haskell 040405/BjL.
-- Some slight changes.

module Pord (Pord(..)) where

class Ord a => Pord a where
   glb :: a -> a -> a
   lub :: a -> a -> a
   lt  :: a -> a -> Bool

-- default definitions:

   glb x y = min x y
   lub x y = max x y
   lt x y  = x <= y

-- Default definition for basic types:

instance Pord Bool

instance Pord Char

instance Pord Int

instance Pord Integer

instance Pord Ordering

-- Tuple types (2- and 3-tuples):

instance (Pord a, Pord b) => Pord (a,b) where
   glb (x1,y1) (x2,y2) = (glb x1 x2, glb y1 y2)
   lub (x1,y1) (x2,y2) = (lub x1 x2, lub y1 y2)
   lt (x1,y1) (x2,y2)  = lt x1 x2 && lt y1 y2

instance (Pord a, Pord b, Pord c) => Pord (a,b,c) where
   glb (x1,y1,z1) (x2,y2,z2) = (glb x1 x2, glb y1 y2, glb z1 z2)
   lub (x1,y1,z1) (x2,y2,z2) = (lub x1 x2, lub y1 y2, lub z1 z2)
   lt (x1,y1,z1) (x2,y2,z2)  = lt x1 x2 && lt y1 y2 && lt z1 z2