From 97577307a16365c61d8ace7528add983e5c8ff02 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Doderlein <jean.baptiste.doderlein@gmail.com>
Date: Thu, 8 Jan 2026 11:24:38 +0100
Subject: [PATCH 1/2] Enable out of bound in slice with negative index

---
 .../rascalmpl/interpreter/result/ElementResult.java | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/org/rascalmpl/interpreter/result/ElementResult.java b/src/org/rascalmpl/interpreter/result/ElementResult.java
index 08e126a7752..781ce034b21 100644
--- a/src/org/rascalmpl/interpreter/result/ElementResult.java
+++ b/src/org/rascalmpl/interpreter/result/ElementResult.java
@@ -229,13 +229,20 @@ public <U extends IValue, V extends IValue> Result<U> slice(Result<?> first, Res
 		
 		if(first != null){
 			firstIndex = getInt(first);
-			if(firstIndex < 0)
-				firstIndex += len;
+			if(firstIndex < 0){
+				firstIndex = Math.max(firstIndex+len, 0);
+			}
+			else{
+				firstIndex = Math.min(firstIndex, len-1);
+			}
 		}
 		if(end != null){
 			endIndex = getInt(end);
 			if(endIndex < 0){
-				endIndex += len;
+				endIndex = Math.max(endIndex+len, 0);
+			}
+			else{
+				endIndex = Math.min(endIndex, len);
 			}
 		}
 		

From f6eec62bef4a24582f7bd8e2738c6519d420efe4 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Doderlein <jean.baptiste.doderlein@gmail.com>
Date: Thu, 8 Jan 2026 15:12:27 +0100
Subject: [PATCH 2/2] Fix issue and add tests

---
 src/org/rascalmpl/interpreter/result/ElementResult.java    | 6 +++++-
 .../rascalmpl/library/lang/rascal/tests/basic/Lists.rsc    | 7 +++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/org/rascalmpl/interpreter/result/ElementResult.java b/src/org/rascalmpl/interpreter/result/ElementResult.java
index 781ce034b21..d4a6661ed87 100644
--- a/src/org/rascalmpl/interpreter/result/ElementResult.java
+++ b/src/org/rascalmpl/interpreter/result/ElementResult.java
@@ -233,7 +233,7 @@ public <U extends IValue, V extends IValue> Result<U> slice(Result<?> first, Res
 				firstIndex = Math.max(firstIndex+len, 0);
 			}
 			else{
-				firstIndex = Math.min(firstIndex, len-1);
+				firstIndex = Math.min(firstIndex, len);
 			}
 		}
 		if(end != null){
@@ -246,6 +246,10 @@ public <U extends IValue, V extends IValue> Result<U> slice(Result<?> first, Res
 			}
 		}
 		
+		if(firstIndex == len && endIndex<firstIndex){
+			firstIndex = len - 1;
+		}
+		
 		if(second == null){
 			secondIndex = firstIndex + ((firstIndex <= endIndex) ? 1 : -1);
 		} else {
diff --git a/src/org/rascalmpl/library/lang/rascal/tests/basic/Lists.rsc b/src/org/rascalmpl/library/lang/rascal/tests/basic/Lists.rsc
index aff8f7b056a..09a476c1c8c 100644
--- a/src/org/rascalmpl/library/lang/rascal/tests/basic/Lists.rsc
+++ b/src/org/rascalmpl/library/lang/rascal/tests/basic/Lists.rsc
@@ -246,6 +246,13 @@ test bool sliceSecondNegative(list[int] L) {
   return S == makeSlice(L, 0, size(L) - incr, size(L));
 }
 
+test bool sliceOutOfBoundIndex1() { L = [0,1,2,3,4,5,6,7,8,9]; return L[..] == [0,1,2,3,4,5,6,7,8,9];}
+test bool sliceOutOfBoundIndex2() { L = [0,1,2,3,4,5,6,7,8,9]; return L[10..] == [];}
+test bool sliceOutOfBoundIndex3() { L = [0,1,2,3,4,5,6,7,8,9]; return L[10..10] == [];}
+test bool sliceOutOfBoundIndex4() { L = [0,1,2,3,4,5,6,7,8,9]; return L[10..-11] == [9,8,7,6,5,4,3,2,1];}
+test bool sliceOutOfBoundIndex5() { L = [0,1,2,3,4,5,6,7,8,9]; return L[-15..-11] == [];}
+test bool sliceOutOfBoundIndex6() { L = [0,1,2,3,4,5,6,7,8,9]; return L[10..-5] == [9,8,7,6];}
+
 test bool assignSlice1() { L = [0,1,2,3,4,5,6,7,8,9]; L[..] = [10,20]; return L == [10,20,10,20,10,20,10,20,10,20];}
 test bool assignSlice2() { L = [0,1,2,3,4,5,6,7,8,9]; L[2..] = [10,20]; return   L == [0,1,10,20,10,20,10,20,10,20];}
 test bool assignSlice3() { L = [0,1,2,3,4,5,6,7,8,9]; L[2..6] = [10,20]; return L == [0,1,10,20,10,20,6,7,8,9];}