diff --git a/CMakeLists.txt b/CMakeLists.txt
index b1f0d65..1c754fc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
-project(fun VERSION 0.41.14 LANGUAGES C)
+project(fun VERSION 0.41.15 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 99)
 set(CMAKE_C_STANDARD_REQUIRED ON)
diff --git a/Doxyfile b/Doxyfile
index 429658f..39f0078 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -48,7 +48,7 @@ PROJECT_NAME           = "Fun API Documentation"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.41.10
+PROJECT_NUMBER         = 0.41.15
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewers a
diff --git a/cmake/Options.cmake b/cmake/Options.cmake
index 8ad1fa5..8992b1c 100644
--- a/cmake/Options.cmake
+++ b/cmake/Options.cmake
@@ -34,6 +34,9 @@ endif()
 # Debug option to enable verbose parser/VM logging
 option(FUN_DEBUG "Enable extra debug logging in Fun" OFF)
 
+# Optional: VM trace and opcode counters (disabled by default)
+option(FUN_TRACE "Enable VM tracing and opcode execution counters" OFF)
+
 # VM settings (configurable via -D...)
 set(MAX_FRAMES 128 CACHE STRING "Maximum depth of the call stack (frames)")
 set(MAX_FRAME_LOCALS 64 CACHE STRING "Maximum number of local variables per frame")
diff --git a/cmake/Targets.cmake b/cmake/Targets.cmake
index 8ce3db9..534d279 100644
--- a/cmake/Targets.cmake
+++ b/cmake/Targets.cmake
@@ -21,6 +21,11 @@ if(FUN_DEBUG)
   target_compile_definitions(fun_core PUBLIC FUN_DEBUG=1)
 endif()
 
+# Enable VM tracing/counters when requested
+if(FUN_TRACE)
+  target_compile_definitions(fun_core PUBLIC FUN_TRACE=1)
+endif()
+
 # Provide default stdlib directory and version to the runtime
 target_compile_definitions(fun_core PUBLIC FUN_VERSION="${PROJECT_VERSION}")
 target_compile_definitions(fun_core PUBLIC DEFAULT_LIB_DIR="${DEFAULT_LIB_DIR}")
diff --git a/src/bytecode.c b/src/bytecode.c
index fd7f95b..27109ef 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -36,16 +36,28 @@ Bytecode *bytecode_new(void) {
 }
 
 /**
- * @brief Append a constant to a Bytecode's constant table.
+ * @brief Append a constant to a Bytecode's constant table with de-duplication.
  *
- * The value is deep-copied into the table; the caller retains ownership of v
- * and may free it independently.
+ * The value is compared against existing constants and if an equal constant is
+ * already present, its index is returned without modifying the table. Equality
+ * uses value_equals which supports numeric cross-type (int/float) equality and
+ * string content equality. The caller retains ownership of @p v in all cases.
+ * When a new constant is inserted, a deep copy is stored in the table.
  *
  * @param bc Target bytecode (must not be NULL).
- * @param v  Value to store (copied).
- * @return The index of the stored constant (zero-based).
+ * @param v  Value to store (copied on insert).
+ * @return The index of the stored or matched existing constant (zero-based).
  */
 int bytecode_add_constant(Bytecode *bc, Value v) {
+  /* Linear scan for a match. This is fast enough for small constant pools and
+   * avoids duplicates (smaller bytecode, better cache locality). */
+  for (int i = 0; i < bc->const_count; ++i) {
+    if (value_equals(&bc->constants[i], &v)) {
+      return i;
+    }
+  }
+
+  /* Not found: append a copy */
   bc->constants = (Value *)realloc(bc->constants, sizeof(Value) * (bc->const_count + 1));
   bc->constants[bc->const_count] = copy_value(&v);
   return bc->const_count++;
diff --git a/src/bytecode.h b/src/bytecode.h
index 8bb4897..42c4aea 100644
--- a/src/bytecode.h
+++ b/src/bytecode.h
@@ -291,6 +291,9 @@ typedef enum {
   OP_CPP_ADD, // pops b, a; pushes (a + b)
 } OpCode;
 
+/* Total number of opcodes (keep in sync with OpCode enum). */
+#define OPCODE_COUNT (OP_CPP_ADD + 1)
+
 typedef struct {
   OpCode op;
   int32_t operand;
diff --git a/src/parser.c b/src/parser.c
index 3346115..eee6572 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -56,9 +56,16 @@ extern char *preprocess_includes_with_path(const char *src, const char *current_
 static void skip_to_eol(const char *src, size_t len, size_t *pos);
 static int read_line_start(const char *src, size_t len, size_t *pos, int *out_indent);
 static void parse_block(Bytecode *bc, const char *src, size_t len, size_t *pos, int current_indent);
+static void calc_line_col(const char *src, size_t len, size_t pos, int *out_line, int *out_col);
 
 /* ---- parser error state ---- */
 static const char *g_current_source_path = NULL; /* for propagating filename into nested bytecodes */
+/* Track active source buffer for error line computation and cascade control */
+static const char *g_active_src = NULL;
+static size_t g_active_len = 0;
+static int g_last_err_line = -1;
+static int g_line_err_count = 0;
+static const int G_ERRS_PER_LINE_CAP = 3; /* suppress floods after this many per line */
 static int g_has_error = 0;
 static size_t g_err_pos = 0;
 static char g_err_msg[256];
@@ -137,6 +144,22 @@ static int fun_debug_enabled(void) {
  * @param ... Arguments matching fmt.
  */
 static void parser_fail(size_t pos, const char *fmt, ...) {
+  /* Optional flood guard: suppress excessive errors on the same source line */
+  if (g_active_src && g_active_len > 0) {
+    int line = 0, col = 0;
+    calc_line_col(g_active_src, g_active_len, pos, &line, &col);
+    if (line == g_last_err_line) {
+      if (g_line_err_count >= G_ERRS_PER_LINE_CAP) {
+        /* Too many errors on this line; ignore to avoid cascades */
+        return;
+      }
+      g_line_err_count++;
+    } else {
+      g_last_err_line = line;
+      g_line_err_count = 1;
+    }
+  }
+
   g_has_error = 1;
   g_err_pos = pos;
   va_list ap;
@@ -7608,8 +7631,16 @@ Bytecode *parse_file_to_bytecode(const char *path) {
   g_err_line = 0;
   g_err_col = 0;
 
-  /* Set current source path for nested bytecodes to inherit */
+  /* Set active source for error mapping/cascade control and current source path for nested bytecodes */
   const char *prev_source = g_current_source_path;
+  const char *prev_active_src = g_active_src;
+  size_t prev_active_len = g_active_len;
+  int prev_last_line = g_last_err_line;
+  int prev_line_count = g_line_err_count;
+  g_active_src = compile_src;
+  g_active_len = compile_len;
+  g_last_err_line = -1;
+  g_line_err_count = 0;
   g_current_source_path = path;
   Bytecode *bc = compile_minimal(compile_src, compile_len);
   /* assign debug metadata to module bytecode */
@@ -7624,6 +7655,10 @@ Bytecode *parse_file_to_bytecode(const char *path) {
   }
   /* restore previous */
   g_current_source_path = prev_source;
+  g_active_src = prev_active_src;
+  g_active_len = prev_active_len;
+  g_last_err_line = prev_last_line;
+  g_line_err_count = prev_line_count;
 
   if (g_has_error) {
     int line = 1, col = 1;
@@ -7791,8 +7826,16 @@ Bytecode *parse_string_to_bytecode(const char *source) {
   g_err_line = 0;
   g_err_col = 0;
 
-  /* Set current source path to <input> for nested bytecodes */
+  /* Set active source for error mapping/cascade control and current source path to <input> for nested bytecodes */
   const char *prev_src = g_current_source_path;
+  const char *prev_active_src = g_active_src;
+  size_t prev_active_len = g_active_len;
+  int prev_last_line = g_last_err_line;
+  int prev_line_count = g_line_err_count;
+  g_active_src = compile_src;
+  g_active_len = len;
+  g_last_err_line = -1;
+  g_line_err_count = 0;
   g_current_source_path = NULL;
   Bytecode *bc = compile_minimal(compile_src, len);
   if (bc) {
@@ -7802,6 +7845,10 @@ Bytecode *parse_string_to_bytecode(const char *source) {
     bc->name = strdup("<input>");
   }
   g_current_source_path = prev_src;
+  g_active_src = prev_active_src;
+  g_active_len = prev_active_len;
+  g_last_err_line = prev_last_line;
+  g_line_err_count = prev_line_count;
 
   if (g_has_error) {
     int line = 1, col = 1;
diff --git a/src/vm.c b/src/vm.c
index 073feb0..f5a3803 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -224,6 +224,8 @@ static void fun_vm_exit(int code) {
 
 /* Forward decl for stack push used by vm_raise_error */
 static void push_value(VM *vm, Value v);
+/* Forward decl for diagnostic helper used by vm_raise_error */
+static int vm_ip_to_line(const Bytecode *bc, int ip);
 
 /* Raise a runtime error that respects try/catch/finally semantics.
  * If a handler is installed for the current frame, jump to it and push
@@ -259,8 +261,22 @@ void vm_raise_error(VM *vm, const char *msg) {
     f->ip = target;
     return;
   }
-  /* No handler: print annotated message and terminate VM */
-  fprintf(stderr, "Runtime error: %s\n", msg ? msg : "<error>");
+  /* No handler: print annotated message, stack trace, and terminate VM */
+  Bytecode *bc = f->fn;
+  const char *fname = (bc && bc->name) ? bc->name : "<anon>";
+  const char *src = (bc && bc->source_file) ? bc->source_file : "<unknown>";
+  int last_ip = f->ip - 1;
+  int line = vm_ip_to_line(bc, last_ip);
+  const char *opname = "OP?";
+  if (bc && last_ip >= 0 && last_ip < bc->instr_count) {
+    int op = bc->instructions[last_ip].op;
+    if (op >= 0 && op < (int)(sizeof(opcode_names) / sizeof(opcode_names[0]))) {
+      opname = opcode_names[op];
+    }
+  }
+  fprintf(stderr, "Runtime error at %s:%d in %s (ip=%d, %s): %s\n",
+          src, line > 0 ? line : 0, fname, last_ip, opname, msg ? msg : "<error>");
+  vm_print_stacktrace(vm);
   vm->fp = -1; /* stop execution */
 }
 
@@ -389,6 +405,11 @@ void vm_reset(VM *vm) {
   // Reset exit code
   vm->exit_code = 0;
 
+#ifdef FUN_TRACE
+  // Reset opcode counters
+  for (int i = 0; i < OPCODE_COUNT; ++i) vm->op_counts[i] = 0;
+#endif
+
   // Reset debugger state (breakpoints, stepping)
   vm_debug_reset(vm);
 }
@@ -732,6 +753,10 @@ void vm_init(VM *vm) {
   vm->repl_on_error = 0;
   vm->on_error_repl = NULL;
 
+#ifdef FUN_TRACE
+  for (int i = 0; i < OPCODE_COUNT; ++i) vm->op_counts[i] = 0;
+#endif
+
   /* Debugger state */
   vm->debug_step_mode = 0;
   vm->debug_step_target_fp = -1;
@@ -812,6 +837,60 @@ void vm_print_output(VM *vm) {
   }
 }
 
+/* ---- Diagnostics helpers ---- */
+/* Find best-effort source line for given ip by scanning backwards for OP_LINE. */
+static int vm_ip_to_line(const Bytecode *bc, int ip) {
+  if (!bc || !bc->instructions || ip < 0) return 0;
+  if (ip >= bc->instr_count) ip = bc->instr_count - 1;
+  for (int i = ip; i >= 0; --i) {
+    if (bc->instructions[i].op == OP_LINE) {
+      return bc->instructions[i].operand;
+    }
+  }
+  return 0;
+}
+
+/* Print a human-readable stack trace (top frame first). */
+void vm_print_stacktrace(VM *vm) {
+  if (!vm) return;
+  fprintf(stderr, "Stack trace (most recent call first):\n");
+  for (int fp = vm->fp; fp >= 0; --fp) {
+    Frame *fr = &vm->frames[fp];
+    Bytecode *bc = fr->fn;
+    const char *fname = (bc && bc->name) ? bc->name : "<anon>";
+    const char *src = (bc && bc->source_file) ? bc->source_file : "<unknown>";
+    int ip = fr->ip - 1; /* last executed */
+    int line = vm_ip_to_line(bc, ip);
+    const char *opname = "OP?";
+    if (bc && ip >= 0 && ip < bc->instr_count) {
+      int op = bc->instructions[ip].op;
+      if (op >= 0 && op < (int)(sizeof(opcode_names) / sizeof(opcode_names[0]))) {
+        opname = opcode_names[op];
+      }
+    }
+    fprintf(stderr, "  at %s:%d in %s (ip=%d, %s)\n", src, line > 0 ? line : 0, fname, ip, opname);
+  }
+}
+
+#ifdef FUN_TRACE
+/**
+ * @brief Dump non-zero opcode execution counters to stdout.
+ */
+void vm_dump_opcode_counters(VM *vm) {
+  if (!vm) return;
+  long long total = 0;
+  for (int i = 0; i < OPCODE_COUNT; ++i) total += vm->op_counts[i];
+  printf("=== opcode counters (total %lld) ===\n", total);
+  for (int i = 0; i < OPCODE_COUNT; ++i) {
+    long long c = vm->op_counts[i];
+    if (c > 0) {
+      const char *name = (i >= 0 && i < (int)(sizeof(opcode_names) / sizeof(opcode_names[0]))) ? opcode_names[i] : "OP?";
+      printf("%3d %-16s %lld\n", i, name, c);
+    }
+  }
+}
+#endif
+
 /**
  * @brief Execute a bytecode program starting from the given entry point.
  *
@@ -886,11 +965,25 @@ void vm_run(VM *vm, Bytecode *entry) {
 
     /* Validate opcode defensively */
     if (!opcode_is_valid(inst.op)) {
-      fprintf(stderr, "Runtime error: invalid opcode %d at ip=%d\n", inst.op, f->ip - 1);
-      vm_raise_error(vm, "Invalid opcode");
+      char buf[256];
+      Bytecode *bc = f->fn;
+      const char *fname = (bc && bc->name) ? bc->name : "<anon>";
+      const char *src = (bc && bc->source_file) ? bc->source_file : "<unknown>";
+      int ip = f->ip - 1;
+      int line = vm_ip_to_line(bc, ip);
+      const char *opname = (inst.op >= 0 && inst.op < (int)(sizeof(opcode_names)/sizeof(opcode_names[0]))) ? opcode_names[inst.op] : "OP?";
+      snprintf(buf, sizeof(buf), "invalid opcode %d (%s) at %s:%d in %s (ip=%d)", inst.op, opname, src, line > 0 ? line : 0, fname, ip);
+      vm_raise_error(vm, buf);
       break;
     }
 
+#ifdef FUN_TRACE
+    /* Increment per-opcode counter */
+    if (inst.op >= 0 && inst.op < OPCODE_COUNT) {
+      vm->op_counts[inst.op]++;
+    }
+#endif
+
     if (vm->trace_enabled) {
       const char *opname = (inst.op >= 0 && inst.op < (int)(sizeof(opcode_names) / sizeof(opcode_names[0])))
                              ? opcode_names[inst.op]
@@ -1205,4 +1298,9 @@ void vm_run(VM *vm, Bytecode *entry) {
     }
   }
   g_active_vm = NULL;
+#ifdef FUN_TRACE
+  if (vm->trace_enabled) {
+    vm_dump_opcode_counters(vm);
+  }
+#endif
 }
diff --git a/src/vm.h b/src/vm.h
index 2c021fd..c76de93 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -121,6 +121,11 @@ struct VM {
   int output_is_partial[OUTPUT_SIZE]; // 1 when the corresponding output entry should not end with newline (echo)
 
   long long instr_count; // executed instructions in the last vm_run
+  
+#ifdef FUN_TRACE
+  /* Per-opcode execution counters (enabled when FUN_TRACE=1) */
+  long long op_counts[OPCODE_COUNT];
+#endif
 
   int current_line; // last executed source line (debug)
 
@@ -163,6 +168,10 @@ void vm_clear_output(VM *vm);
  * @param vm VM instance.
  */
 void vm_print_output(VM *vm);
+/** Dump per-opcode execution counters (when FUN_TRACE enabled). */
+void vm_dump_opcode_counters(VM *vm);
+/** Print a human-readable VM stack trace to stderr (top frame first). */
+void vm_print_stacktrace(VM *vm);
 /**
  * @brief Free all resources owned by the VM (globals, frames, output buffers).
  * The VM object itself is not freed when allocated on the stack.
diff --git a/src/vm/arithmetic/add.c b/src/vm/arithmetic/add.c
index 3da5df2..c31bdeb 100644
--- a/src/vm/arithmetic/add.c
+++ b/src/vm/arithmetic/add.c
@@ -33,6 +33,7 @@
  */
 
 case OP_ADD: {
+  vm_require_stack(vm, 2);
   Value b = pop_value(vm);
   Value a = pop_value(vm);
   if ((a.type == VAL_INT || a.type == VAL_FLOAT) && (b.type == VAL_INT || b.type == VAL_FLOAT)) {
diff --git a/src/vm/core/dup.c b/src/vm/core/dup.c
index fc6c95f..606d5a7 100644
--- a/src/vm/core/dup.c
+++ b/src/vm/core/dup.c
@@ -28,10 +28,7 @@
  */
 
 case OP_DUP: {
-  if (vm->sp < 0) {
-    fprintf(stderr, "Runtime error: stack underflow for DUP\n");
-    exit(1);
-  }
+  vm_require_stack(vm, 1);
   Value top = vm->stack[vm->sp];
   push_value(vm, copy_value(&top));
   break;
diff --git a/src/vm/core/pop.c b/src/vm/core/pop.c
index 5cc3d02..ecf96b2 100644
--- a/src/vm/core/pop.c
+++ b/src/vm/core/pop.c
@@ -26,10 +26,7 @@
  */
 
 case OP_POP: {
-  if (vm->sp < 0) {
-    fprintf(stderr, "Runtime error: stack underflow for POP\n");
-    exit(1);
-  }
+  vm_require_stack(vm, 1);
   Value v = pop_value(vm);
   free_value(v);
   break;
diff --git a/src/vm/core/swap.c b/src/vm/core/swap.c
index 8cf2488..c3df3a7 100644
--- a/src/vm/core/swap.c
+++ b/src/vm/core/swap.c
@@ -23,10 +23,7 @@
  */
 
 case OP_SWAP: {
-  if (vm->sp < 1) {
-    fprintf(stderr, "Runtime error: stack underflow for SWAP\n");
-    exit(1);
-  }
+  vm_require_stack(vm, 2);
   Value a = vm->stack[vm->sp];
   Value b = vm->stack[vm->sp - 1];
   vm->stack[vm->sp] = b;