gistfile1.sh

hs [master●] % ghci                                                       ~/workspace/folone.github.com/docs/hs
GHCi, version 7.6.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :l NewYear
[1 of 1] Compiling Main             ( NewYear.hs, interpreted )
Ok, modules loaded: Main.
*Main> :t congratulation
congratulation :: Happy NewYear
*Main> congratulation
Happy (NewYear 2013)
*Main> bonusCongratulation 
("Happy New Year",2013)
*Main> :q
Leaving GHCi.

NewYear.hs

import Control.Applicative

data NewYear = NewYear Int
               deriving (Eq, Show)
data Happy a = Happy a
               deriving (Eq, Show)

instance Functor Happy where
  fmap f (Happy a) = Happy $ f a

instance Applicative Happy where
   pure = Happy
   (Happy f) <*> (Happy x) = Happy (f x)

from :: Int -> Happy Int
from = pure . (+ 1)

congratulation :: Happy NewYear
congratulation  = Happy NewYear <*> from 2012

-- http://stackoverflow.com/questions/10937268/applicative-instance-for-a-tuple-with-monoid-and-function-inside
bonusCongratulation = ("Happy ", (*)) <*> ("New ", 671) <*> ("Year", 3)