haskell - 如何使用镜头语法检查地图是否有键？

Question

如何使用镜头语法检查地图是否有键？

import qualified Map as Map

let x = Map.member "bla" m

如何用镜头写这个？

score 4 · Accepted Answer

4

使用has.

M.fromList [("bla", ())] & has (ix "bla")

于 2014-02-27T21:33:04.483 回答

score 1 · Accepted Answer

>>> Map.fromList [("bla", ())] ^. contains "bla"
True

>>> Map.fromList [("bla", ())] & contains "bla" .~ False
Map.fromList []

2 回答 2