在Haskell中访问Graph数据类型的成员

Question

我的问题很简单，例如，我真的是函数编程领域的新手，所以我想知道如何访问数据类型的元素以创建一个空图。

module Graph where

import Data.Map (Map)

import Graphviz

-- | A directed graph
data Graph v = Graph
    { arcsMap :: Map v [v]     -- A map associating a vertex with its successors
    , labelMap :: Map v String -- The Graphviz label of each node
    , styleMap :: Map v String -- The Graphviz style of each node
    }

-- | Returns an empty graph
emptyGraph :: Graph v
emptyGraph = ???

谢谢！

Answer 1

import Data.Map (Map, empty)

-- | A directed graph
data Graph v = Graph
   { arcsMap :: Map v [v]     -- A map associating a vertex with its successors
   , labelMap :: Map v String -- The Graphviz label of each node
   , styleMap :: Map v String -- The Graphviz style of each node
   }

-- | Returns an empty graph
emptyGraph :: Graph v
emptyGraph = Graph empty empty empty