src/Hakyll/Core/DirectedGraph/Internal.hs · hakyll

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1-- | Internal structure of the DirectedGraph type. Not exported in the library.

2--

3module Hakyll.Core.DirectedGraph.Internal

4 ( Node (..)

5 , DirectedGraph (..)

6 ) where

8import Prelude hiding (reverse, filter)

9import Data.Monoid (Monoid, mempty, mappend)

10import Data.Set (Set)

11import Data.Map (Map)

12import qualified Data.Map as M

13import qualified Data.Set as S

15-- | A node in the directed graph

17data Node a = Node

18 { nodeTag :: a -- ^ Tag identifying the node

19 , nodeNeighbours :: (Set a) -- ^ Edges starting at this node

20 } deriving (Show)

22-- | Append two nodes. Useful for joining graphs.

24appendNodes :: Ord a => Node a -> Node a -> Node a

25appendNodes (Node t1 n1) (Node t2 n2)

26 | t1 /= t2 = error "appendNodes: Appending differently tagged nodes"

27 | otherwise = Node t1 (n1 `S.union` n2)

29-- | Type used to represent a directed graph

31newtype DirectedGraph a = DirectedGraph {unDirectedGraph :: Map a (Node a)}

32 deriving (Show)

34-- | Allow users to concatenate different graphs

36instance Ord a => Monoid (DirectedGraph a) where

37 mempty = DirectedGraph M.empty

38 mappend (DirectedGraph m1) (DirectedGraph m2) = DirectedGraph $

39 M.unionWith appendNodes m1 m2