[Haskell-cafe] Query

hi i am going through yaht tutorial and exercise 4.6 and 4.7..i understood 4.6,but not 4.7 in which fromTuple (One a ) = Left (Left a ) and fromTuple (Two a b ) = Left (Right (a,b) ) function r written..why use Either type..cant i just say fromTuple (Two a b )=(a,b)