indent n = concat $ replicate n "  "

gen level n max
    | level == max = indent level ++ "a := '" ++ (show $ product [1..n]) ++  "'\n"
    | otherwise = indent level ++ "if n <= " ++ show (n+2^(max-level-1)) ++  " then\n" ++
                  gen (level+1) n max ++
                  indent level ++ "else\n" ++
                  gen (level+1) (n+2^(max-level-1)) max

main = putStrLn $ gen 0 0 6