verify graph paths incl laws graph

Logic/Graph.hs

@@ -38,6 +38,8 @@ Just ["add","double","add","double","double","add"]
 
 data VerifyPathError vertex edge
   = NoSuchEdge vertex edge
+  | GoalNotReached [vertex]
+  deriving Show
 
 verifyPath
   :: (Eq vertex, Ord vertex, Eq edge)
@@ -45,11 +47,22 @@ verifyPath
   -> vertex
   -> vertex
   -> [edge]
-  -> Either (VerifyPathError vertex edge) Bool
+  -> Either (VerifyPathError vertex edge) [vertex]
 verifyPath getEdges goal start path =
-  case path of
-    [] -> Right $ start == goal
-    (thisEdge:nextEdges) ->
-      case map fst $ filter (\(next, realEdge) -> realEdge == thisEdge) $ getEdges start of
-        [] -> Left $ NoSuchEdge start thisEdge
-        (next:_) -> verifyPath getEdges goal next nextEdges
+  case aux start path of
+    Right (vertices, True) -> Right vertices
+    Right (vertices, False) -> Left $ GoalNotReached vertices
+    Left x -> Left x
+  where
+    aux vertex path' = cons vertex <$>
+      case path' of
+        [] -> Right $
+          if vertex == goal
+          then ([], True)
+          else ([], False)
+        (thisEdge:nextEdges) ->
+          case map fst $ filter (\(next, realEdge) -> realEdge == thisEdge) $ getEdges vertex of
+            [] -> Left $ NoSuchEdge vertex thisEdge
+            (next:_) -> aux next nextEdges
+
+    cons vertex (vertices, bool) = (vertex:vertices, bool)

Logic/Statement/Laws.hs

@@ -4,7 +4,7 @@ import Logic.Parse (eof, mkInput)
 import Logic.Statement (Statement(..))
 import Logic.Statement.Parse (stmt)
 import Logic.Statement.Serialize (serialize, SerializeFormat(Plain))
-import Logic.Graph (bfs)
+import Logic.Graph (bfs, verifyPath, VerifyPathError)
 
 import Data.Either (fromRight, rights)
 import Data.Maybe (fromJust, listToMaybe)
@@ -220,16 +220,25 @@ firstLeft [] = Right []
 firstLeft ((Left a):_) = Left a
 firstLeft ((Right b):xs) = (b:) <$> firstLeft xs
 
+data Direction
+  = Forward
+  | Reverse
+  deriving (Eq, Show)
+
 data LawsGraphEdge = LawsGraphEdge
-  { lgeLaw :: Law
-  , lgeReverse :: Bool
+  { lgeDirection :: Direction
   , lgeIndex :: Integer
+  , lgeLaw :: Law
   } deriving Eq
 
 instance Show LawsGraphEdge where
   show edge =
     "LawsGraphEdge{"
-    <> (if lgeReverse edge then "< " else "> ")
+    <> (
+      case lgeDirection edge of
+        Forward -> "> "
+        Reverse -> "< "
+    )
     <> lawName (lgeLaw edge)
     <> " "
     <> show (lgeIndex edge)
@@ -246,27 +255,26 @@ getLawsGraphEdges s = concat $ rights $ map aux laws
   where
     aux :: Law -> Either ReplaceError [(Statement, LawsGraphEdge)]
     aux law = do
-      forward <- direction law lawLhs lawRhs False
-      reverse <- direction law lawRhs lawLhs True
+      forward <- edges Forward law
+      reverse <- edges Reverse law
       return $ forward ++ reverse
 
-    direction
-      :: Law
-      -> (Law -> Statement)
-      -> (Law -> Statement)
-      -> Bool
-      -> Either ReplaceError [(Statement, LawsGraphEdge)]
-    direction law mkPattern1 mkPattern2 isReverse = do
-      replaceds <- replace (mkPattern1 law) (mkPattern2 law) s
-      return $
-        (flip map) (zip [0..] replaceds) $ \(index, s') ->
-          let
-            edge = LawsGraphEdge
-              { lgeLaw = law
-              , lgeReverse = isReverse
-              , lgeIndex = index
-              }
-          in (s', edge)
+    replaceds :: Direction -> Law -> Either ReplaceError [Statement]
+    replaceds direction law =
+      let
+        (pattern1, pattern2) =
+          case direction of
+            Forward -> (lawLhs law, lawRhs law)
+            Reverse -> (lawRhs law, lawLhs law)
+      in replace pattern1 pattern2 s
+
+    mkEdges :: Direction -> Law -> [Statement] -> [(Statement, LawsGraphEdge)]
+    mkEdges direction law statements = do
+      (index, s') <- zip [0..] statements
+      return (s', LawsGraphEdge direction index law)
+
+    edges :: Direction -> Law -> Either ReplaceError [(Statement, LawsGraphEdge)]
+    edges direction law = mkEdges direction law <$> replaceds direction law
 
 {-
 ghci> fromString x = fromRight undefined $ eof stmt $ mkInput x
@@ -314,3 +322,34 @@ ghci> time $ putStrLn $ show $ niceEdges <$> bfsLaws (fromString "!!!!!!!!!!!!p"
 Just ["> dbl_neg 0","> dbl_neg 0","> dbl_neg 0","> dbl_neg 0","> dbl_neg 0","> dbl_neg 0"]
 3066.211460539s
 -}
+
+data LawsGraphPath = LawsGraphPath
+  { lgpStart :: Statement
+  , lgpGoal :: Statement
+  , lgpEdges :: [LawsGraphEdge]
+  } deriving Show
+
+verifyLawsPath
+  :: LawsGraphPath
+  -> Either (VerifyPathError Statement LawsGraphEdge) [Statement]
+verifyLawsPath path =
+  verifyPath getLawsGraphEdges (lgpGoal path) (lgpStart path) (lgpEdges path)
+
+lawsPathExample1 :: LawsGraphPath
+lawsPathExample1 = LawsGraphPath start goal edges
+  where
+    start = Implies (Atom "p") (Atom "q")
+    goal = Implies (Not (Atom "q")) (Not (Atom "p"))
+    edges =
+      [ LawsGraphEdge Forward 1 $ law "dbl_neg"
+      , LawsGraphEdge Forward 0 $ law "implies_and"
+      , LawsGraphEdge Forward 0 $ law "and_comm"
+      , LawsGraphEdge Reverse 0 $ law "implies_and"
+      ]
+    law = fromJust . lookupLaw
+
+{-
+ghci> import Logic.Statement.Serialize (serialize, SerializeFormat(..))
+ghci> map (serialize Plain) <$> verifyLawsPath lawsPathExample1
+Right ["(p->q)","(!!p->q)","!(!!p&!q)","!(!q&!!p)","(!q->!p)"]
+-}

Logic/readme.md

@@ -9,6 +9,7 @@ things that are in here:
 ### [Logic.Graph](Graph.hs)
 
 - generic breadth-first search
+- verify graph paths reach the goal and have all extant edges
 
 ## statement things
 
@@ -38,7 +39,7 @@ things that are in here:
 ### [Logic.Statements.Laws](Statements/Laws.hs)
 
 - match/replace patterns in statements (e.g. logical laws)
-- verify logical-law equivalence of statements (TODO)
+- verify logical-law equivalence of statements
 - find logical-law equivalence of statements with breadth-first search (slow)
 
 ### [Logic.Language](Language.hs)