Allow function calls in expressions and add len() built-in

- Parse function calls in parse_term() so they work inside expressions
  (e.g. z = len(x), y = len(x) + 1)
- Add len() built-in for string length in evaluator

src/frontend/parser.h

@@ -65,6 +65,8 @@ ASTNode *make_node(NodeType type) {
 
 int pos = 0;
 
+ASTNode *parse_expr(Token *tokens);
+
 ASTNode *parse_term(Token *tokens) {
   if (tokens[pos].type == TOK_INT) {
     ASTNode *node = make_node(NODE_INT_LIT);
@@ -77,8 +79,32 @@ ASTNode *parse_term(Token *tokens) {
     pos++;
     return node;
   } else if (tokens[pos].type == TOK_ID) {
-    printf("Parsing token: %s\n", tokens[pos].value);
+    if (tokens[pos +1].type == TOK_LPAREN) {
+      // Function call
+      char *name = tokens[pos].value;
+      pos++; // consumir ID
+      pos++; // consumir (
 
+      // Parsear argumentos
+      ASTNode **args =
+          (ASTNode **)malloc(sizeof(ASTNode *) * 16); // Max 16 parametros
+      int arg_count = 0;
+
+      if (tokens[pos].type != TOK_RPAREN) {
+        args[arg_count++] = parse_expr(tokens);
+        while (tokens[pos].type == TOK_COMMA) {
+          pos++; // Consumir ","
+          args[arg_count++] = parse_expr(tokens);
+        }
+      }
+      pos++; // consumir ")"
+      ASTNode *node = make_node(NODE_CALL);
+      node->data.call.name = name;
+      node->data.call.args = args;
+      node->data.call.arg_count = arg_count;
+      return node;
+
+    }
     ASTNode *node = make_node(NODE_VAR);
     node->data.string_val = tokens[pos].value;
     pos++;