From 95b270416709717696e3cd1cbab143f1b19590dc Mon Sep 17 00:00:00 2001
From: Martin Eberlein <33397273+martineberlein@users.noreply.github.com>
Date: Mon, 6 Feb 2023 18:39:40 +0100
Subject: [PATCH] Update expansion_key to handle empty alternatives
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When using the ProbabilisticGrammarMiner to learn the probability distribution from a set of given inputs, the miner does not return the correct probabilistic grammar. In particular, this bug occurs whenever a grammar is used with a production rule that has an "empty" alternative: ⟨maybe_minus⟩ ::= "" | "-". Somehow the miner does not account for the empty ("") derivation sequence. See Issue #153
---
 docs/code/GrammarCoverageFuzzer.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/code/GrammarCoverageFuzzer.py b/docs/code/GrammarCoverageFuzzer.py
index 78320e11e..2118ebfde 100755
--- a/docs/code/GrammarCoverageFuzzer.py
+++ b/docs/code/GrammarCoverageFuzzer.py
@@ -196,6 +196,10 @@ def expansion_key(symbol: str,
     if isinstance(expansion, tuple):
         # Expansion or single derivation tree
         expansion, _ = expansion
+        
+    # Check for empty list expansion
+    if isinstance(expansion, list) and not expansion:
+        expansion = ""
 
     if not isinstance(expansion, str):
         # Derivation tree