A personal study note after http://en.wikibooks.org/wiki/Programming:Haskell_monads

monadwiki.hs

module Monadwiki
where

{-
A personal study note after
http://en.wikibooks.org/wiki/Programming:Haskell_monads
-}

data Person = Person { name::String, father::Maybe Person, mother::Maybe Person }
  deriving (Show,Eq)

ore = Person {
  name="Ore",
  father = Just Person {
    name="Oyaji",
    father=Just Person {
      name="Oyaji-no-Oyaji",
      father=Nothing,
      mother=Nothing
    },
    mother=Nothing
  },
  mother = Just Person {
    name="Ofukuro",
    father= Just Person {
      name="Ofukuro-no-Oyaji",
      father=Nothing,
      mother=Nothing
    },
    mother=Nothing
  }
}

{- monad example shown on the page -}
mgf p = mother p >>= father

{- my example -}
myMgf p = let m = mother p
          in
            case m of
              Nothing -> Nothing
              Just b -> father b