Add string type support: literals, concatenation, println, and if eval

- Implement string literal tokenization and parsing (lexer + parser)
- Add string concatenation with + operator in evaluator
- Add println keyword for printing with newline
- Add NODE_IF evaluation in VM
- Fix null terminator bug in string concat buffer

src/vm/eval.h

@@ -54,6 +54,8 @@ size_t eval(ASTNode *node, Environment *env, void *allocator, int debug,
   }
 
   switch (node->type) {
+  case NODE_STRING_LIT:
+    return obj_new_string(allocator, node->data.string_val);
   case NODE_INT_LIT:
     return obj_new_int(allocator, node->data.int_val);
   case NODE_VAR:
@@ -73,6 +75,22 @@ size_t eval(ASTNode *node, Environment *env, void *allocator, int debug,
 
     // Operar (ints por ahora)
     if (node->data.binop.op == '+') {
+      if (l->type == OBJ_STRING) {
+        int n = l->data.string_val.length + r->data.string_val.length;
+        char *tempBuff = (char *)malloc(n + 1);
+        // Copy left text
+        memcpy(tempBuff, JLANG_RESOLVE(allocator, l->data.string_val.chars),
+               l->data.string_val.length);
+
+        // Copy right text
+        memcpy(tempBuff + l->data.string_val.length, JLANG_RESOLVE(allocator, r->data.string_val.chars),
+               r->data.string_val.length);
+        tempBuff[n] = '\0';
+
+        size_t newObj = obj_new_string(allocator, tempBuff);
+        free(tempBuff);
+        return newObj;
+      }
       return obj_new_int(allocator, l->data.int_val + r->data.int_val);
     } else if (node->data.binop.op == '-') {
       return obj_new_int(allocator, l->data.int_val - r->data.int_val);
@@ -87,6 +105,11 @@ size_t eval(ASTNode *node, Environment *env, void *allocator, int debug,
     }
   }
   case NODE_PRINT: {
+    size_t val = eval(node->data.print.expr, env, allocator, debug, gc);
+    obj_print(allocator, val, "");
+    return val;
+  }
+  case NODE_PRINTLN: {
     size_t val = eval(node->data.print.expr, env, allocator, debug, gc);
     obj_print(allocator, val, "");
     printf("\n");
@@ -101,7 +124,7 @@ size_t eval(ASTNode *node, Environment *env, void *allocator, int debug,
       }
       gc_collect(allocator, roots, env->count);
     }
-    
+
     for (int i = 0; i < node->data.block.count; i++)
       eval(node->data.block.stmts[i], env, allocator, debug, gc);
     return 0;
@@ -113,6 +136,15 @@ size_t eval(ASTNode *node, Environment *env, void *allocator, int debug,
         break;
       eval(node->data.while_loop.body, env, allocator, debug, gc);
     }
+    return 0;
+  case NODE_IF: {
+    size_t cond = eval(node->data.while_loop.cond, env, allocator, debug, gc);
+    Object *obj = (Object *)JLANG_RESOLVE(allocator, cond);
+    if (obj->data.int_val > 0) {
+      eval(node->data.while_loop.body, env, allocator, debug, gc);
+    }
+    break;
+  }
   default:
     break;
   }