prune top left and bottom right of L-NFA when possible

breandan · Oct 26, 2024 · ab5d42a · ab5d42a
1 parent 19322b3
commit ab5d42a
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Showing 2 changed files with 13 additions and 7 deletions.
diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/FLTheory.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/FLTheory.kt
@@ -45,12 +45,18 @@ fun pruneInactiveRules(cfg: CFG): CFG =
   TODO("Identify and prune all nonterminals t generating" +
     "a finite language rooted at t and disjoint from the upward closure.")
 
-fun CFG.maxParsableFragment(tokens: List<String>, padRight: Int = 3): Int =
-  (1..tokens.size).first { i ->
-    val blocked = tokens.mapIndexed { j, t -> if (j < i) t else "_" } + List(padRight) { "_" }
+fun CFG.maxParsableFragment(tokens: List<String>, pad: Int = 3): Pair<Int, Int> =
+  ((1..tokens.size).firstOrNull { i ->
+    val blocked =
+      tokens.mapIndexed { j, t -> if (j < i) t else "_" } + List(pad) { "_" }
 //    println(blocked)
     blocked !in language
-  }
+  } ?: tokens.size) to ((2..tokens.size).firstOrNull { i ->
+    val blocked = List(pad) { "_" } +
+        tokens.mapIndexed { j, t -> if (tokens.size - i < j) t else "_" }
+//    println(blocked)
+    blocked !in language
+  }?.let { tokens.size - it } ?: 0)
 
 // REL ⊂ CFL ⊂ CJL
 operator fun REL.contains(s: Σᐩ): Bln = s in reg.asCFG.language

diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Levenshtein.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Levenshtein.kt
@@ -62,7 +62,7 @@ fun makeLevFSA(
   str: List<Σᐩ>,
   dist: Int,
   digits: Int = (str.size * dist).toString().length,
-  lastGoodIndex: Int = str.size
+  bounds: Pair<Int, Int> = str.size to 0
 ): FSA =
   (upArcs(str, dist, digits) +
     diagArcs(str, dist, digits) +
@@ -71,12 +71,12 @@ fun makeLevFSA(
     .also {
       println("Levenshtein-${str.size}x$dist automaton had ${it.size} arcs initially!")
     }.filter { arc ->
-      arc.first.unpackCoordinates().let { (i, j) -> 0 < j || i <= lastGoodIndex + 1 }
+      listOf(arc.first.unpackCoordinates(), arc.third.unpackCoordinates())
+        .all { (i, j) -> (0 < j || i <= bounds.first) && (j < dist || i >= bounds.second - 2) }
     }
     .let { Q ->
       val initialStates = setOf("q_" + pd(0, digits).let { "$it/$it" })
 
-
       val finalStates = mutableSetOf<String>()
       Q.states.forEach {
         val (i, j) = it.unpackCoordinates()