haskell 的一些教学可以参考：

https://www.seas.upenn.edu/~cis194/fall16/index.html

CodeWorld：可以在线运行hs代码，基于ghc.js，四舍五入还是在本地跑

https://code.world/haskell

下面是利用 CodeWorld 画圆的小例子

import CodeWorld

main :: IO()
main = do
       drawingOf $ circle 1

运算符函数

(!!) 取第n个元素

Prelude> :t (!!)
(!!) :: [a] -> Int -> a

Prelude> [0,1,2,3,4]!!3
3
Prelude> [0,1,2,3,4]!!0
0

乘方 (^), (^^),(**)

Prelude> :t (^)
(^) :: (Integral b, Num a) => a -> b -> a
Prelude> 54.5^5
4.8081998590625e8

Prelude> :t (^^)
(^^) :: (Fractional a, Integral b) => a -> b -> a
Prelude> 5.6^^6
30840.979455999986

Prelude> :t (**)
(**) :: Floating a => a -> a -> a
Prelude> 0.2**0.1
0.8513399225207846