Haskell:对于Map中的每个(k,v),用k和v做IO()

Question

我有一个Map (Int,Int) Char,我试图Char在密钥中包含的位置绘制每个s.我的职责是:

import qualified Data.Map.Strict as SM
data Position = Position !GLint !GLint

drawMirrors :: SM.Map (Int,Int) Char -> IO()
drawMirrors mirrors = do
    mapM_ (\(x,y) c -> drawMirror c (Position x y)) mirrors

drawMirror :: Char -> Position -> IO()
drawMirror orientation (Position x y) = do
    -- Some irrelevant stuff

在drawMirrors mirrors = do mapM_ (\(x,y) c -> drawMirror c (Position x y)) mirrors行,我得到的错误:

src\Main.hs:200:33:

Couldn't match expected type `Char -> IO ()'
            with actual type `IO b0'
The lambda expression `\ (x, y) c -> drawMirror c (Position y)'
has two arguments,
but its type `(t0, GLint) -> IO b0' has only one
In the first argument of `mapM_', namely
  `(\ (x, y) c -> drawMirror c (Position y))'
In a stmt of a 'do' block:
  mapM_ (\ (x, y) c -> drawMirror c (Position y)) mirrors

如何drawMirrors获取字典中的所有键和值并drawMirror使用这些键和值应用函数？

Answer 1

你的lambda,\(x,y) c -> drawMirror c (Position x y)有两个参数.但是,它使用表单的一个参数调用(key, value)(在您的情况下)((x, y), c).

(\((x,y), c) -> drawMirror c (Position x y))

而且,mapM_(我相信你的情况来自Data.Foldable)只迭代键,所以你可能想调用SM.toList一个列表(key, value).

最终结果是:

drawMirrors :: SM.Map (Int,Int) Char -> IO()
drawMirrors mirrors = do
    mapM_ (\((x,y), c) -> drawMirror c (Position x y)) $ SM.toList mirrors