feat(library/vm): add is_vm_builtin_function

src/library/vm.cpp

@@ -342,6 +342,10 @@ void declare_vm_builtin(name const & n, unsigned arity, vm_function fn) {
     g_vm_builtins->insert(n, mk_pair(arity, fn));
 }
 
+bool is_vm_builtin_function(name const & fn) {
+    return g_vm_builtins->contains(fn);
+}
+
 /** \brief VM function/constant declarations are stored in an environment extension. */
 struct vm_decls : public environment_extension {
     bool               m_initialized;

src/library/vm.h

@@ -341,6 +341,9 @@ environment optimize_vm_decls(environment const & env);
 /** \brief Return true iff \c fn is a VM function in the given environment. */
 bool is_vm_function(environment const & env, name const & fn);
 
+/** \brief Return true iff \c fn is implemented in C++. */
+bool is_vm_builtin_function(name const & fn);
+
 void initialize_vm();
 void finalize_vm();
 }