이게 이해가 안 되는데 어떡하지?

[기괴공학도(mecheng98)]

import qualified Data.Set as Set

import qualified Data.Map.Strict as Map

getTSortedSCCs :: Ord node => Map.Map node (Set.Set node) → [Set.Set node]

getTSortedSCCs digraph = snd (spanningSearch getIns (Set.empty, []) (snd (depthFirstSearch getOuts (Set.empty, []) getVertices))) where

___ depthFirst rel (visted, sorted) cur

___ ___ | cur `Set.member` visited = (visited, sorted)

___ ___ | otherwise = case depthFirstSearch rel (Set.inset cur visited, sorted) (rel cur) of

___ ___ ___ (visited', sorted') → (visited', cur : sorted')

___ spanning rel (visted, sccs) cur

___ ___ | cur `Set.member` visited = (visited, sccs)

___ ___ | otherwise = case depthFirstSearch rel (Set.insert cur visited, []) (rel cur) of

___ ___ ___ (visited', sorted') → (visited', Set.fromList (cur : sorted') : sccs)

___ getVertices = map fst (Map.toList digraph)

___ getIns node = [ node' | (node', nodes) ← Map.toList digraph, node `Set.member` nodes ]

___ getOuts node = Set.toList (fromJust (Map.lookup node digraph))

___ depthFirstSearch = foldl . depthFirst

___ spanningSearch = foldl . spanning

유향그래프를 넣으면 SCC들의 위상정렬된 리스트가 나오는 이유 좀 설명해주셈 ㅇㅅㅇ

- dc official App