From d7fe6a8dda6860241ac11662ddf7a60f836b0e89 Mon Sep 17 00:00:00 2001
From: breandan <bre@ndan.co>
Date: Mon, 16 Oct 2023 11:23:19 -0400
Subject: [PATCH] implement more efficient pruner (TODO)

---
 .../ai/hypergraph/kaliningraph/parsing/BarHillel.kt       | 2 +-
 .../ai/hypergraph/kaliningraph/parsing/Normalization.kt   | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
index fb0a0310..c0003c86 100644
--- a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
+++ b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
@@ -112,7 +112,7 @@ fun CFG.dropVestigialProductions(
 //  val reachable = reachableSymbols()
   val rw = toMutableSet()
     .apply { removeAll { prod -> prod.RHS.any { criteria(it) && it !in nts } } }
-    .freeze().removeUselessSymbols()
+    .freeze().removeUselessSymbols()//.removeUnreachable().freeze().removeNonGenerating()
 
   println("Removed ${size - rw.size} vestigial productions.")
 
diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
index 23247856..2412b554 100644
--- a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
+++ b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
@@ -161,6 +161,7 @@ fun CFG.refactorEpsilonProds(nlbls: Set<Σᐩ> = nullableNonterminals()): CFG =
  * A useful symbol is both generating and reachable.
  */
 
+// TODO: https://zerobone.net/blog/cs/non-productive-cfg-rules/
 fun CFG.removeUselessSymbols(
   generating: Set<Σᐩ> = genSym(),
   reachable: Set<Σᐩ> = reachSym()
@@ -180,6 +181,13 @@ fun CFG.removeUselessSymbols(
 //  }
 //  .first.toSet()
 
+//fun CFG.removeNonGenerating(generating: Set<Σᐩ> = genSym()) =
+//  toMutableSet().apply { removeAll { (s, _) -> s !in generating } }
+//
+//fun CFG.removeUnreachable() =
+//  toMutableSet().apply { removeAll { (s, _) -> !reachableNTs[bindex[s]] } }
+//    .also { println("Removed ${size - it.size} unreachable productions.") }
+
 fun CFG.equivalenceClass(from: Σᐩ): Set<Σᐩ> = unitReachability[from] ?: setOf(from)
 
 fun LabeledGraph.transitiveClosure(from: Set<Σᐩ>) =