pyramid.hs

makePyramid :: Int -> [String]
makePyramid h | h < 1     = []
              | otherwise = [makeLine n | n <- numbers]
  where
    numbers    = take h [x | x <- [1..], odd x]
    l          = last numbers
    makeLine n =  spaces ++ asters ++ spaces
      where
        numOfSpaces = (l - n) `div` 2
        spaces      = [' ' | _ <- [1 .. numOfSpaces]]
        asters      = ['*' | _ <- [1 .. n]]

printPyramid :: Int -> IO ()
printPyramid n = mapM_ putStrLn $ makePyramid n