From 8653146512cbeddedbb06bee73445d1c1d9505f7 Mon Sep 17 00:00:00 2001
From: maxonfjvipon <mtrunnikov@gmail.com>
Date: Mon, 18 Mar 2024 12:36:04 +0300
Subject: [PATCH 1/3] fix(#2924): grammar

---
 eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4 b/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
index b266a2259b..4f2519de59 100644
--- a/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
+++ b/eo-parser/src/main/antlr4/org/eolang/parser/Phi.g4
@@ -58,7 +58,7 @@ emptyBinding
     ;
 
 deltaBidning
-    : DELTA DASHED_ARROW BYTES
+    : DELTA DASHED_ARROW (BYTES | EMPTY)
     ;
 
 lambdaBidning

From 30ee02be242353311ad5eb47a96cda0e3297ba21 Mon Sep 17 00:00:00 2001
From: maxonfjvipon <mtrunnikov@gmail.com>
Date: Mon, 18 Mar 2024 12:40:29 +0300
Subject: [PATCH 2/3] fix(#2924): throw

---
 .../src/main/java/org/eolang/parser/XePhiListener.java     | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/eo-parser/src/main/java/org/eolang/parser/XePhiListener.java b/eo-parser/src/main/java/org/eolang/parser/XePhiListener.java
index a509d8a3cc..cb576abcac 100644
--- a/eo-parser/src/main/java/org/eolang/parser/XePhiListener.java
+++ b/eo-parser/src/main/java/org/eolang/parser/XePhiListener.java
@@ -313,6 +313,13 @@ public void exitEmptyBinding(final PhiParser.EmptyBindingContext ctx) {
 
     @Override
     public void enterDeltaBidning(final PhiParser.DeltaBidningContext ctx) {
+        if (ctx.EMPTY() != null) {
+            throw new ParsingException(
+                "It's impossible to represent Δ ⤍ ∅ binding in EO",
+                new IllegalStateException(),
+                ctx.getStart().getLine()
+            );
+        }
         this.objects()
             .start()
             .prop("data", "bytes")

From fe423f938b9ece88e010d6623841c1442c34ea84 Mon Sep 17 00:00:00 2001
From: maxonfjvipon <mtrunnikov@gmail.com>
Date: Mon, 18 Mar 2024 13:19:02 +0300
Subject: [PATCH 3/3] fix(#2924): test

---
 .../src/test/java/org/eolang/parser/PhiSyntaxTest.java | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/eo-parser/src/test/java/org/eolang/parser/PhiSyntaxTest.java b/eo-parser/src/test/java/org/eolang/parser/PhiSyntaxTest.java
index 5739c0925b..5161f8dd77 100644
--- a/eo-parser/src/test/java/org/eolang/parser/PhiSyntaxTest.java
+++ b/eo-parser/src/test/java/org/eolang/parser/PhiSyntaxTest.java
@@ -26,6 +26,7 @@
 import com.jcabi.matchers.XhtmlMatchers;
 import java.io.IOException;
 import org.hamcrest.MatcherAssert;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.xembly.Directives;
 
@@ -48,6 +49,15 @@ void addsError() throws IOException {
         );
     }
 
+    @Test
+    void catchesDeltaToNothingBinding() throws IOException {
+        Assertions.assertThrows(
+            ParsingException.class,
+            new PhiSyntax("{ ⟦ x ↦ ⟦ Δ ⤍ ∅ ⟧ ⟧ }")::parsed,
+            "Impossible binding with Δ should be caught"
+        );
+    }
+
     @Test
     void addsExtra() throws IOException {
         MatcherAssert.assertThat(