diff --git a/include/cubescript/cubescript.hh b/include/cubescript/cubescript.hh
index b20e2c5..aa69661 100644
--- a/include/cubescript/cubescript.hh
+++ b/include/cubescript/cubescript.hh
@@ -211,7 +211,6 @@ struct LIBCUBESCRIPT_EXPORT ident {
     int get_raw_type() const;
     ident_type get_type() const;
     std::string_view get_name() const;
-    int get_flags() const;
     int get_index() const;
 
     bool is_alias() const;
@@ -243,13 +242,14 @@ struct LIBCUBESCRIPT_EXPORT ident {
 protected:
     ident() = default;
 
-private:
     friend struct state;
 
     ident_impl *p_impl{};
 };
 
 struct LIBCUBESCRIPT_EXPORT global_var: ident {
+    bool is_read_only() const;
+
 protected:
     global_var() = default;
 };
@@ -279,6 +279,8 @@ protected:
 };
 
 struct LIBCUBESCRIPT_EXPORT alias: ident {
+    bool is_arg() const;
+
 protected:
     alias() = default;
 };
diff --git a/src/cs_ident.cc b/src/cs_ident.cc
index defc89f..abd45e5 100644
--- a/src/cs_ident.cc
+++ b/src/cs_ident.cc
@@ -142,10 +142,6 @@ LIBCUBESCRIPT_EXPORT std::string_view ident::get_name() const {
     return p_impl->p_name;
 }
 
-LIBCUBESCRIPT_EXPORT int ident::get_flags() const {
-    return p_impl->p_flags;
-}
-
 LIBCUBESCRIPT_EXPORT int ident::get_index() const {
     return p_impl->p_index;
 }
@@ -270,6 +266,10 @@ LIBCUBESCRIPT_EXPORT string_var const *ident::get_svar() const {
     return static_cast<string_var const *>(this);
 }
 
+LIBCUBESCRIPT_EXPORT bool global_var::is_read_only() const {
+    return (p_impl->p_flags & IDENT_FLAG_READONLY);
+}
+
 LIBCUBESCRIPT_EXPORT integer_type integer_var::get_value() const {
     return static_cast<ivar_impl const *>(this)->p_storage;
 }
@@ -294,6 +294,10 @@ LIBCUBESCRIPT_EXPORT void string_var::set_value(string_ref val) {
     static_cast<svar_impl *>(this)->p_storage = val;
 }
 
+LIBCUBESCRIPT_EXPORT bool alias::is_arg() const {
+    return (static_cast<alias_impl const *>(this)->p_flags & IDENT_FLAG_ARG);
+}
+
 LIBCUBESCRIPT_EXPORT std::string_view command::get_args() const {
     return static_cast<command_impl const *>(this)->p_cargs;
 }
diff --git a/src/cs_state.cc b/src/cs_state.cc
index a80cb6e..55682c1 100644
--- a/src/cs_state.cc
+++ b/src/cs_state.cc
@@ -330,7 +330,7 @@ LIBCUBESCRIPT_EXPORT void state::set_alias(
             case ident_type::ALIAS: {
                 alias *a = static_cast<alias *>(id);
                 auto &ast = p_tstate->get_astack(a);
-                if (a->get_flags() & IDENT_FLAG_ARG) {
+                if (a->is_arg()) {
                     ast.set_arg(a, *p_tstate, v);
                 } else {
                     ast.set_alias(a, *p_tstate, v);
@@ -421,7 +421,7 @@ state::get_alias_val(std::string_view name) {
     if (!a) {
         return std::nullopt;
     }
-    if ((a->get_flags() & IDENT_FLAG_ARG) && !ident_is_used_arg(a, *p_tstate)) {
+    if (a->is_arg() && !ident_is_used_arg(a, *p_tstate)) {
         return std::nullopt;
     }
     return p_tstate->get_astack(a).node->val_s.get_str();
@@ -566,10 +566,7 @@ LIBCUBESCRIPT_EXPORT void state::run(
             }
             case ident_type::ALIAS: {
                 alias *a = static_cast<alias *>(id);
-                if (
-                    (a->get_flags() & IDENT_FLAG_ARG) &&
-                    !ident_is_used_arg(a, *p_tstate)
-                ) {
+                if (a->is_arg() && !ident_is_used_arg(a, *p_tstate)) {
                     break;
                 }
                 exec_alias(
diff --git a/src/cs_vm.cc b/src/cs_vm.cc
index c6a737e..9c4e84a 100644
--- a/src/cs_vm.cc
+++ b/src/cs_vm.cc
@@ -10,7 +10,7 @@
 namespace cubescript {
 
 static inline void push_alias(thread_state &ts, ident *id, ident_stack &st) {
-    if (id->is_alias() && !(id->get_flags() & IDENT_FLAG_ARG)) {
+    if (id->is_alias() && !static_cast<alias *>(id)->is_arg()) {
         auto *aimp = static_cast<alias_impl *>(id);
         ts.get_astack(aimp).push(st);
         aimp->p_flags &= ~IDENT_FLAG_UNKNOWN;
@@ -18,7 +18,7 @@ static inline void push_alias(thread_state &ts, ident *id, ident_stack &st) {
 }
 
 static inline void pop_alias(thread_state &ts, ident *id) {
-    if (id->is_alias() && !(id->get_flags() & IDENT_FLAG_ARG)) {
+    if (id->is_alias() && !static_cast<alias *>(id)->is_arg()) {
         ts.get_astack(static_cast<alias *>(id)).pop();
     }
 }
@@ -285,13 +285,13 @@ run_depth_guard::~run_depth_guard() { --rundepth; }
 
 static inline alias *get_lookup_id(thread_state &ts, std::uint32_t op) {
     ident *id = ts.istate->identmap[op >> 8];
+    auto *a = static_cast<alias_impl *>(id);
 
-    auto flags = id->get_flags();
-    if (flags & IDENT_FLAG_ARG) {
+    if (a->is_arg()) {
         if (!ident_is_used_arg(id, ts)) {
             return nullptr;
         }
-    } else if (flags & IDENT_FLAG_UNKNOWN) {
+    } else if (a->p_flags & IDENT_FLAG_UNKNOWN) {
         throw error{
             *ts.pstate, "unknown alias lookup: %s", id->get_name().data()
         };
@@ -308,17 +308,16 @@ static inline int get_lookupu_type(
     id = ts.pstate->get_ident(arg.get_str());
     if (id) {
         switch(id->get_type()) {
-            case ident_type::ALIAS:
-                if (id->get_flags() & IDENT_FLAG_UNKNOWN) {
+            case ident_type::ALIAS: {
+                auto *a = static_cast<alias_impl *>(id);
+                if (a->p_flags & IDENT_FLAG_UNKNOWN) {
                     break;
                 }
-                if (
-                    (id->get_flags() & IDENT_FLAG_ARG) &&
-                    !ident_is_used_arg(id, ts)
-                ) {
+                if (a->is_arg() && !ident_is_used_arg(id, ts)) {
                     return ID_UNKNOWN;
                 }
                 return ID_ALIAS;
+            }
             case ident_type::SVAR:
                 return ID_SVAR;
             case ident_type::IVAR:
@@ -745,10 +744,7 @@ std::uint32_t *vm_exec(
                 alias *a = static_cast<alias *>(
                     ts.istate->identmap[op >> 8]
                 );
-                if (
-                    (a->get_flags() & IDENT_FLAG_ARG) &&
-                    !ident_is_used_arg(a, ts)
-                ) {
+                if (a->is_arg() && !ident_is_used_arg(a, ts)) {
                     ts.get_astack(a).push(ts.idstack.emplace_back(*ts.pstate));
                     ts.callstack->usedargs[a->get_index()] = true;
                 }
@@ -761,11 +757,8 @@ std::uint32_t *vm_exec(
                 if (arg.get_type() == value_type::STRING) {
                     id = cs.new_ident(arg.get_str(), IDENT_FLAG_UNKNOWN);
                 }
-                if (
-                    (id->get_flags() & IDENT_FLAG_ARG) &&
-                    !ident_is_used_arg(id, ts)
-                ) {
-                    auto *a = static_cast<alias *>(id);
+                alias *a = static_cast<alias *>(id);
+                if (a->is_arg() && !ident_is_used_arg(id, ts)) {
                     ts.get_astack(a).push(ts.idstack.emplace_back(*ts.pstate));
                     ts.callstack->usedargs[id->get_index()] = true;
                 }
@@ -1022,7 +1015,7 @@ std::uint32_t *vm_exec(
                     ts.istate->identmap[op >> 8]
                 );
                 auto &ast = ts.get_astack(a);
-                if (a->get_flags() & IDENT_FLAG_ARG) {
+                if (a->is_arg()) {
                     ast.set_arg(a, ts, args.back());
                 } else {
                     ast.set_alias(a, ts, args.back());
@@ -1047,21 +1040,21 @@ std::uint32_t *vm_exec(
                 std::size_t callargs = *code++;
                 std::size_t nnargs = args.size();
                 std::size_t offset = nnargs - callargs;
-                auto flags = id->get_flags();
-                if (flags & IDENT_FLAG_ARG) {
+                auto *imp = static_cast<alias_impl *>(id);
+                if (imp->is_arg()) {
                     if (!ident_is_used_arg(id, ts)) {
                         args.resize(offset, any_value{cs});
                         force_arg(result, op & BC_INST_RET_MASK);
                         continue;
                     }
-                } else if (flags & IDENT_FLAG_UNKNOWN) {
+                } else if (imp->p_flags & IDENT_FLAG_UNKNOWN) {
                     force_arg(result, op & BC_INST_RET_MASK);
                     throw error{
                         cs, "unknown command: %s", id->get_name().data()
                     };
                 }
                 exec_alias(
-                    ts, static_cast<alias *>(id), &args[0], result, callargs,
+                    ts, imp, &args[0], result, callargs,
                     nnargs, offset, 0, op
                 );
                 args.resize(nnargs, any_value{cs});
@@ -1197,10 +1190,7 @@ noid:
                     }
                     case ID_ALIAS: {
                         alias *a = static_cast<alias *>(id);
-                        if (
-                            (a->get_flags() & IDENT_FLAG_ARG) &&
-                            !ident_is_used_arg(a, ts)
-                        ) {
+                        if (a->is_arg() && !ident_is_used_arg(a, ts)) {
                             args.resize(offset - 1, any_value{cs});
                             force_arg(result, op & BC_INST_RET_MASK);
                             continue;
diff --git a/src/lib_base.cc b/src/lib_base.cc
index 86a7729..c7a005b 100644
--- a/src/lib_base.cc
+++ b/src/lib_base.cc
@@ -159,7 +159,7 @@ void init_lib_base(state &gcs) {
 
     gcs.new_command("pushif", "rte", [](auto &cs, auto args, auto &res) {
         if (alias_local st{cs, args[0].get_ident()}; st) {
-            if (st.get_alias()->get_flags() & IDENT_FLAG_ARG) {
+            if (st.get_alias()->is_arg()) {
                 return;
             }
             if (args[1].get_bool()) {
@@ -304,7 +304,7 @@ end:
 
     gcs.new_command("push", "rte", [](auto &cs, auto args, auto &res) {
         if (alias_local st{cs, args[0].get_ident()}; st) {
-            if (st.get_alias()->get_flags() & IDENT_FLAG_ARG) {
+            if (st.get_alias()->is_arg()) {
                 return;
             }
             st.set(args[1]);