Added line numbers to debug and error output.

examples/objects_more.fun

@@ -12,9 +12,9 @@
 // Objects as maps: nested fields, methods with explicit self
 
 // A method to move a 2D point by dx, dy
-fun move(self, dx, dy)
+fun move(p, x, y)
-  self["x"] = self["x"] + dx
+  p["x"] = p["x"] + x
-  self["y"] = self["y"] + dy
+  p["y"] = p["y"] + y
   return 0
 
 // Create a point directly and inspect fields

src/bytecode.h

@@ -46,6 +46,8 @@ typedef enum {
     OP_PRINT,
     OP_HALT,
 
+    OP_LINE,         // operand = source line number (debug marker)
+
     // add after existing opcodes
     OP_MOD,          // a % b
     OP_AND,      // logical AND

src/parser.c

@@ -1736,6 +1736,13 @@ static void parse_block(Bytecode *bc, const char *src, size_t len, size_t *pos,
         }
 
         /* at same indent -> parse statement */
+        /* Insert a line marker for better runtime error reporting */
+        {
+            int stmt_line = 1, stmt_col = 1;
+            calc_line_col(src, len, line_start, &stmt_line, &stmt_col);
+            bytecode_add_instruction(bc, OP_LINE, stmt_line);
+        }
+
         if (starts_with(src, len, *pos, "fun")) {
             /* parse header: fun name(arg, ...) */
             *pos += 3;

src/vm.c

@@ -16,6 +16,34 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdarg.h>
+
+/* Track the currently running VM to annotate error messages */
+static VM *g_active_vm = NULL;
+
+/* fprintf wrapper that appends source line info for stderr messages */
+static int fun_vm_vfprintf(FILE *stream, const char *fmt, va_list ap) {
+    int written = vfprintf(stream, fmt, ap);
+    if (stream == stderr && g_active_vm && g_active_vm->current_line > 0) {
+        /* If original message didn't end with newline, add a space first */
+        if (written > 0) {
+            /* best-effort: do not attempt to inspect fmt string fully; just append line info */
+        }
+        fprintf(stream == stderr ? stderr : stream, " (line %d)\n", g_active_vm->current_line);
+    }
+    return written;
+}
+
+static int fun_vm_fprintf(FILE *stream, const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int r = fun_vm_vfprintf(stream, fmt, ap);
+    va_end(ap);
+    return r;
+}
+
+/* Redirect fprintf within this translation unit so opcode handlers use our wrapper */
+#define fprintf fun_vm_fprintf
 
 /*
 Opcode case include index (vm_case_*.inc):
@@ -178,6 +206,8 @@ void vm_print_output(VM *vm) {
 void vm_run(VM *vm, Bytecode *entry) {
     /* reset instruction count for this run */
     vm->instr_count = 0;
+    vm->current_line = 1;
+    g_active_vm = vm;
 
     /* start with entry frame (no args) */
     vm_push_frame(vm, entry, 0, NULL);
@@ -266,6 +296,7 @@ void vm_run(VM *vm, Bytecode *entry) {
             #include "vm/strings/substr.c"
 
             #include "vm/len.c"
+            #include "vm/line.c"
             #include "vm/print.c"
             #include "vm/to_number.c"
             #include "vm/to_string.c"
@@ -283,4 +314,5 @@ void vm_run(VM *vm, Bytecode *entry) {
                 break;
         }
     }
+    g_active_vm = NULL;
 }

src/vm.h

@@ -32,6 +32,7 @@ static const char *opcode_names[] = {
     "LOAD_GLOBAL","STORE_GLOBAL","ADD","SUB","MUL","DIV",
     "LT","LTE","GT","GTE","EQ","NEQ","POP","JUMP",
     "JUMP_IF_FALSE","CALL","RETURN","PRINT","HALT",
+    "LINE",
     "MOD","AND","OR","NOT","DUP","SWAP",
     "MAKE_ARRAY","INDEX_GET","INDEX_SET",
     "LEN","PUSH","APOP","SET","INSERT","REMOVE","SLICE",
@@ -63,6 +64,8 @@ typedef struct {
     int output_count;
 
     long long instr_count; // executed instructions in the last vm_run
+
+    int current_line; // last executed source line (debug)
 } VM;
 
 // initialize VM (zero state)

src/vm/line.c

@@ -0,0 +1,5 @@
+case OP_LINE: {
+    /* operand holds the source line number */
+    vm->current_line = inst.operand;
+    break;
+}