Complete VM parity with eval and fix operator precedence

VM: add string concatenation in OP_ADD, len() built-in, multi-arg
print/println, undefined variable detection, and GC via OP_NOP.
Parser: fix operator precedence by splitting into parse_expr (+,-)
and parse_term (*,/) so 8 + 2 * 4 = 16 instead of 40.
Compiler: emit OP_NOP at start of NODE_BLOCK to trigger GC.

projects/vm_simple.j

@@ -1,6 +1,2 @@
-x = 0
-while x < 10:
-    x = x + 1
-
-if x > 1000000:
-    println("OK")
+x = 8 + 2 * 4
+print(x, end="\n")

projects/while.j

@@ -1,4 +1,5 @@
 x = 0
-while x < 1000000000:
+while x < 10000000:
     x = x + 1
-println(x)
+print(x)
+debugHeap()

src/backend/bytecode/compiler.h

@@ -85,6 +85,9 @@ int compile_node(Chunk *chunk, ASTNode* node) {
         case NODE_BLOCK: {
             int n = node->data.block.count;
             
+            // NOP for gc
+            emit(chunk, make_instruction(OP_NOP));
+
             for (int i=0; i<n; i++){
                 compile_node(chunk, node->data.block.stmts[i]);
             }
@@ -156,6 +159,7 @@ int compile_node(Chunk *chunk, ASTNode* node) {
             chunk->code[jump_offset].operand.jump_target = chunk->code_count;
             break;
         }
+        
         default:
             break;
     }

src/backend/bytecode/vm.h

@@ -5,7 +5,6 @@
 #include "compiler.h"
 #include "value.h"
 
-
 typedef struct {
   Chunk *chunk;
   int ip; // instruction pointer
@@ -77,6 +76,10 @@ void run_vm(VM *vm) {
     case OP_LOAD_VAR: {
       // get from vm->var
       int idx = instr.operand.var_index;
+      if (!vm->var_set[idx]) {
+        printf("error: variable '%s' no definida\n", vm->chunk->names[idx]);
+        return;
+      }
       Value v = vm->vars[idx];
       // push to stack
       vm->stack[vm->sp++] = v;
@@ -87,8 +90,11 @@ void run_vm(VM *vm) {
       int nameIdx = instr.operand.call.name_index;
 
       char *name = vm->chunk->names[nameIdx];
-      if (strcmp(name, "print") == 0) {
-        Value v = vm->stack[--vm->sp];
+      if (strcmp(name, "print") == 0 || strcmp(name, "println") == 0) {
+
+        int nParams = instr.operand.call.arg_count;
+        for (int i = 0; i < nParams; i++) {
+          Value v = vm->stack[vm->sp - nParams + i];
           switch (v.type) {
           case VAL_INT:
             printf("%d", v.as.int_val);
@@ -96,26 +102,37 @@ void run_vm(VM *vm) {
           case VAL_OBJ: {
             // Get object from heap
             obj_print(vm->allocator, v.as.heap_offset, "", "");
+            break;
           }
           default:
             break;
           }
-      } else if (strcmp(name, "println") == 0) {
-        Value v = vm->stack[--vm->sp];
-        switch (v.type) {
-        case VAL_INT:
-          printf("%d\n", v.as.int_val);
-          break;
-        case VAL_OBJ: {
-          // Get object from heap
-          obj_print(vm->allocator, v.as.heap_offset, "", "\n");
         }
-        default:
-          break;
+        vm->sp -= nParams;
+
+        if (strcmp(name, "println") == 0) {
+          printf("\n");
         }
-      } else if (strcmp(name, "debug_heap") == 0) {
+
+      } else if (strcmp(name, "debugHeap") == 0) {
+        printf("\n");
         JLANG_visualize(vm->allocator);
         break;
+      } else if (strcmp(name, "len") == 0) {
+        // pop value from stack
+        Value var1 = vm->stack[--vm->sp];
+        if (var1.type == VAL_OBJ) {
+          // Resolve obj
+          Object *obj = JLANG_RESOLVE(vm->allocator, var1.as.heap_offset);
+
+          Value result = {0};
+          result.type = VAL_INT;
+          result.as.int_val = obj->data.string_val.length;
+
+          // push to stack
+          vm->stack[vm->sp++] = result;
+        }
+        break;
       } else {
         printf("error: function '%s' not found!\n", name);
         return;
@@ -129,9 +146,41 @@ void run_vm(VM *vm) {
       Value var2 = vm->stack[--vm->sp];
       Value var1 = vm->stack[--vm->sp];
 
+      if (var1.type != var2.type) {
+        printf("panic: var types mismatch on OP_ADD\n");
+        return;
+      }
+
       Value result = {0};
+
+      if (var1.type == VAL_INT) {
         result.type = VAL_INT;
         result.as.int_val = var1.as.int_val + var2.as.int_val;
+      } else if (var1.type == VAL_OBJ) {
+        // resolve obj
+        Object *obj1 = JLANG_RESOLVE(vm->allocator, var1.as.heap_offset);
+        Object *obj2 = JLANG_RESOLVE(vm->allocator, var2.as.heap_offset);
+
+        // get chars
+        char *str1 = JLANG_RESOLVE(vm->allocator, obj1->data.string_val.chars);
+        char *str2 = JLANG_RESOLVE(vm->allocator, obj2->data.string_val.chars);
+
+        // tmp char buffer
+        size_t total =
+            obj1->data.string_val.length + obj2->data.string_val.length;
+        char *tmpBuffer = (char *)malloc(total + 1);
+        memcpy(tmpBuffer, str1, obj1->data.string_val.length);
+        memcpy(tmpBuffer + obj1->data.string_val.length, str2,
+               obj2->data.string_val.length);
+        tmpBuffer[total] = '\0';
+
+        // Create new str
+        size_t strHeapIndex = obj_new_string(vm->allocator, tmpBuffer);
+        free(tmpBuffer);
+        // set value
+        result.type = VAL_OBJ;
+        result.as.heap_offset = strHeapIndex;
+      }
 
       // Push to stack
       vm->stack[vm->sp++] = result;
@@ -208,6 +257,27 @@ void run_vm(VM *vm) {
       break;
     }
 
+    case OP_NOP: {
+      // Pass gc
+      size_t roots[512];
+      int root_count = 0;
+
+      for (int i = 0; i < 256; i++) {
+        if (vm->var_set[i] && vm->vars[i].type == VAL_OBJ) {
+          roots[root_count++] = vm->vars[i].as.heap_offset;
+        }
+      }
+
+      for (int i = 0; i < vm->sp; i++) {
+        if (vm->stack[i].type == VAL_OBJ) {
+          roots[root_count++] = vm->stack[i].as.heap_offset;
+        }
+      }
+
+      gc_collect(vm->allocator, roots, root_count);
+      
+      break;
+    }
     default:
       break;
     }

src/frontend/parser.h

@@ -65,8 +65,11 @@ ASTNode *make_node(NodeType type) {
 int pos = 0;
 
 ASTNode *parse_expr(Token *tokens);
+ASTNode *parse_term(Token *tokens);
+ASTNode *parse_factor(Token *tokens);
 
-ASTNode *parse_term(Token *tokens) {
+
+ASTNode *parse_factor(Token *tokens) {
   if (tokens[pos].type == TOK_INT) {
     ASTNode *node = make_node(NODE_INT_LIT);
     node->data.int_val = atoi(tokens[pos].value);
@@ -133,7 +136,6 @@ ASTNode *parse_expr(Token *tokens) {
   ASTNode *left = parse_term(tokens);
 
   while (tokens[pos].type == TOK_PLUS || tokens[pos].type == TOK_MINUS ||
-         tokens[pos].type == TOK_STAR || tokens[pos].type == TOK_SLASH ||
          tokens[pos].type == TOK_LT || tokens[pos].type == TOK_GT) {
     char op = tokens[pos].value[0]; // +,-,*,/
     pos++;
@@ -148,6 +150,23 @@ ASTNode *parse_expr(Token *tokens) {
   return left;
 }
 
+ASTNode *parse_term(Token *tokens) {
+  ASTNode *left = parse_factor(tokens);
+
+  while (tokens[pos].type == TOK_STAR || tokens[pos].type == TOK_SLASH) {
+    char op = tokens[pos].value[0];
+    pos++;
+    ASTNode *right = parse_factor(tokens);
+
+    ASTNode *binop = make_node(NODE_BINOP);
+    binop->data.binop.op = op;
+    binop->data.binop.left = left;
+    binop->data.binop.right = right;
+    left = binop;
+  }
+  return left;
+}
+
 ASTNode *parse_statement(Token *tokens) {
   if (tokens[pos].type == TOK_ID) {
     if (tokens[pos + 1].type == TOK_LPAREN) {