Jump into REPL when executing with --repl-on-error and an error occurs, when the REPL is builtin you will have access to the full stack then. (0.25.0)

examples/repl_on_error.fun

@@ -0,0 +1,42 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://hanez.org/project/fun/
+ *
+ * Copyright 2025 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ * Added: 2025-10-06
+ */
+
+// Demonstration of --repl-on-error debugging.
+// Run: fun --repl-on-error examples/repl_on_error.fun
+// When the runtime error occurs, the REPL opens. Try commands:
+//   :backtrace
+//   :stack
+//   :locals
+//
+// This script triggers an index-out-of-range error inside a nested call.
+
+fun inner()
+  a = [1, 2, 3]
+  // Out-of-range access to cause a runtime error:
+  print(a[10])
+
+fun outer()
+  inner()
+
+outer()
+
+/* Expected output (ruuning with --repl-on-error you will end up in the REPL 
+ * with full stack access; :backtrace, :stack and :locals):
+Runtime error: index out of range
+ (at ./examples/repl_on_error.fun:12 in inner, op INDEX_GET @ip 9)
+Entering REPL due to runtime error (code 1)
+ (at ./examples/repl_on_error.fun:12 in inner, op INDEX_GET @ip 9)
+Fun 0.25.0 REPL
+Type :help for commands. Submit an empty line to run.
+fun>
+*/