↻ /prog/ Challenge [Vol. λfx.f x] ↻

THE CHALLENGE: Write a program that, given a number n, prints the expansion of (a+b)^n.

Example: 4 → a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4

HOWEVER: You must do the above in a language you do not have any experience with. Never programmed in Haskell before? Gather some documentation and go for it.

_{(Well, you're advised to do that. I can't possibly know whether or not you know a programming language.)}

import System
import Data.List

pascalsTriangle = iterate (\l -> zipWith (+) (0:l) (l++[0])) [1]

aPlusBToTheNthPower n =
    intercalate " + " $ foldl1 (zipWith (++))
        ["": (map show $ init $ tail $ pascalsTriangle !! n) ++ [""], powers "a",
                                                                      reverse $ powers "b"]
    where powers variable =
              "": variable: map ((variable ++) . ('^':) . show) [2..n] 

main =
    do [n] <- getArgs
       print $ aPlusBToTheNthPower $ read n