✨ add special variable "arg"

src/nasal_codegen.cpp

@@ -1091,7 +1091,18 @@ const error& codegen::compile(parse& parse, linker& import) {
     fileindex = 0;
     file = import.filelist().data();
     in_iterloop.push(0);
+
+    // add special symbol globals, which is a hash stores all global variables
     add_symbol("globals");
+    // add special symbol arg here, which is used to store function arguments
+    // for example:
+    //     var f = func(a) {print(arg)}
+    //     f(1, 2, 3);
+    // then the arg is [2, 3], because 1 is accepted by "a"
+    // so in fact "f" is the same as:
+    //     var f = func(a, arg...) {return(arg)}
+    add_symbol("arg");
+
     find_symbol(parse.tree()); // search symbols first
     gen(op_intg, global.size(), 0);
     block_gen(parse.tree()); // generate main block