diff --git a/luprex/core/cpp/globaldb.cpp b/luprex/core/cpp/globaldb.cpp
index 89020293..c85aa72f 100644
--- a/luprex/core/cpp/globaldb.cpp
+++ b/luprex/core/cpp/globaldb.cpp
@@ -45,14 +45,15 @@ LuaDefine(global_table, "globalname", "get a table where global data can be stor
     LuaRet globaltab;
     LuaVar globaldb;
     LuaStack LS(L, globalname, globaltab, globaldb);
+    LS.checkstring(globalname);
 
     // Get a pointer to the globaldb.
     LS.rawget(globaldb, LuaRegistry, "globaldb");
-    if (!LS.istable(globaldb)) {
-        return lua_yield(L, 0); // donotpredict
-    }
 
-    LS.checkstring(globalname);
+    // nopredict
+    if (lua_isyieldable(L) && (!LS.istable(globaldb))) {
+        return lua_yield(L, 0);
+    }
 
     // Get the globaltab from the globaldb, sanity check it.
     LS.rawget(globaltab, globaldb, globalname);
diff --git a/luprex/core/cpp/lpxserver.cpp b/luprex/core/cpp/lpxserver.cpp
index 0ef4e595..0095ece3 100644
--- a/luprex/core/cpp/lpxserver.cpp
+++ b/luprex/core/cpp/lpxserver.cpp
@@ -20,11 +20,13 @@ using ClientVector = eng::vector<UniqueClient>;
 
 class LpxServer : public DrivenEngine {
 public:
+    using StringVec = LuaConsole::StringVec;
     UniqueWorld master_;
     LuaConsole console_;
     ClientVector clients_;
     PrintChanneler print_channeler_;
     int64_t admin_id_;
+    Gui gui_;
 
 public:
     virtual void event_init(int argc, char *argv[]) {
@@ -61,6 +63,22 @@ public:
         stdostream() << "Syntax Error: " << words[1] << std::endl;
     }
 
+    void do_menu_command(const StringVec &cmd) {
+        int64_t place = sv::to_int64(cmd[1], admin_id_);
+        master_->update_gui(admin_id_, place, &gui_);
+        stdostream() << gui_.menu_debug_string();
+    }
+
+    void do_choose_command(const StringVec &cmd) {
+        eng::string action = gui_.get_action(sv::to_int64(cmd[1]));
+        if (action == "") {
+            stdostream() << "Invalid menu item #" << std::endl;
+            return;
+        }
+        stdostream() << "Invoking plan: " << action << std::endl;
+        master_->invoke(Invocation(Invocation::KIND_PLAN, admin_id_, gui_.place(), action));
+    }
+
     void do_tick_command(const util::StringVec &words) {
         master_->invoke(Invocation(Invocation::KIND_TICK, admin_id_, admin_id_, ""));
     }
@@ -78,6 +96,8 @@ public:
         else if (words[0] == "luainvoke") do_luainvoke_command(words);
         else if (words[0] == "luaprobe") do_luaprobe_command(words);
         else if (words[0] == "syntax") do_syntax_command(words);
+        else if (words[0] == "menu") do_menu_command(words);
+        else if (words[0] == "choose") do_choose_command(words);
         else if (words[0] == "tick") do_tick_command(words);
         else if (words[0] == "cpl") do_cpl_command(words);
         else if (words[0] == "quit") do_quit_command(words);
diff --git a/luprex/core/cpp/pprint.cpp b/luprex/core/cpp/pprint.cpp
index 2b4d22f4..eada8c22 100644
--- a/luprex/core/cpp/pprint.cpp
+++ b/luprex/core/cpp/pprint.cpp
@@ -120,8 +120,8 @@ static void tabify(Inspector &insp, int level) {
 
 static void pprint_r(Inspector &insp, int level, LuaSlot root) {
     lua_checkstack(insp.L, 20);
-    LuaVar idv, pairs, key, val;
-    LuaStack LS(insp.L, idv, pairs, key, val);
+    LuaVar idv, pairs, key, val, nextseq;
+    LuaStack LS(insp.L, idv, pairs, key, val, nextseq);
 
     // If it's anything but a table, use 'atomic_print'.
     if (!LS.istable(root)) {
@@ -175,9 +175,9 @@ static void pprint_r(Inspector &insp, int level, LuaSlot root) {
     }
 
     // State variables.
-    int nextseq = 1;
     bool needcomma = false;
     bool multiline = false;
+    LS.set(nextseq, 1);
 
     // Open the brackets.
     (*insp.stream) << "{";
@@ -190,10 +190,10 @@ static void pprint_r(Inspector &insp, int level, LuaSlot root) {
         LS.rawget(val, pairs, i+1);
         if (needcomma) (*insp.stream) << ",";
         needcomma = true;
-        if (LS.isnumber(key) && (LS.ckint(key) == nextseq)) {
+        if (LS.rawequal(key, nextseq)) {
             (*insp.stream) << " ";
             pprint_r(insp, level + 1, val);
-            nextseq = nextseq + 1;
+            LS.set(nextseq, LS.ckinteger(nextseq) + 1);
         } else {
             multiline = true;
             tabify(insp, level + 1);
@@ -227,7 +227,7 @@ static void pprint_r(Inspector &insp, int level, LuaSlot root) {
     // Close the brackets.
     if (multiline) {
         tabify(insp, level);
-    } else if (nextseq > 1) {
+    } else if (LS.ckinteger(nextseq) > 1) {
         (*insp.stream) << " ";
     }
     (*insp.stream) << "}";
diff --git a/luprex/core/cpp/sched.cpp b/luprex/core/cpp/sched.cpp
index dbdaaaf8..6075668b 100644
--- a/luprex/core/cpp/sched.cpp
+++ b/luprex/core/cpp/sched.cpp
@@ -24,6 +24,8 @@ eng::string SchedEntry::debug_string() const {
 }
 
 void Schedule::add(int64_t clk, int64_t thid, int64_t plid) {
+    assert(plid != 0);
+    assert(thid != 0);
     schedule_.insert(SchedEntry(clk, thid, plid));
 }
 
diff --git a/luprex/core/cpp/source.cpp b/luprex/core/cpp/source.cpp
index fede292a..2ea0f15c 100644
--- a/luprex/core/cpp/source.cpp
+++ b/luprex/core/cpp/source.cpp
@@ -328,9 +328,10 @@ static eng::string source_load_lfunctions(lua_State *L) {
         
         // Call the closure.  If there's an error, collect it.
         lua_pushvalue(L, closure.index());
-        if (traceback_pcall(L, 0, 0) != 0) {
-            lua_replace(L, err.index());
-            errss << LS.ckstring(err);
+        eng::string msg = traceback_pcall(L, 0, 0);
+        if (!msg.empty()) {
+            LS.set(err, msg);
+            errss << msg << std::endl;
         }
     }
     LS.result();
@@ -380,9 +381,10 @@ void SourceDB::run_unittests() {
         LS.rawget(func, unittests, name);
 
         lua_pushvalue(L, func.index());
-        if (traceback_pcall(L, 0, 0) != 0) {
-            lua_replace(L, err.index());
-            std::cerr << LS.ckstring(err);
+        eng::string msg = traceback_pcall(L, 0, 0);
+        if (!msg.empty()) {
+            LS.set(err, msg);
+            std::cerr << msg << std::endl;
             any = true;
         }
     }
diff --git a/luprex/core/cpp/traceback.cpp b/luprex/core/cpp/traceback.cpp
index f5fd9d3e..3f454acd 100644
--- a/luprex/core/cpp/traceback.cpp
+++ b/luprex/core/cpp/traceback.cpp
@@ -76,12 +76,19 @@ int traceback_coroutine(lua_State *L) {
 }
 
 
-int traceback_pcall(lua_State *L, int narg, int nret) {
+eng::string traceback_pcall(lua_State *L, int narg, int nret) {
     int status;
     int base = lua_gettop(L) - narg; /* function index */
     lua_pushcfunction(L, traceback_coroutine); /* push traceback function */
     lua_insert(L, base);             /* put it under chunk and args */
     status = lua_pcall(L, narg, nret, base);
     lua_remove(L, base); /* remove traceback function */
-    return status;
+    if (status != LUA_OK) {
+        const char *msg = lua_tostring(L, -1);
+        if ((msg == NULL) || (msg[0] == 0)) {
+            msg = "unknown error";
+        }
+        return msg;
+    }
+    return "";
 }
diff --git a/luprex/core/cpp/traceback.hpp b/luprex/core/cpp/traceback.hpp
index 20d58f8e..fb6e6bbb 100644
--- a/luprex/core/cpp/traceback.hpp
+++ b/luprex/core/cpp/traceback.hpp
@@ -22,9 +22,11 @@ int traceback_coroutine(lua_State *L);
 
 // traceback_pcall
 //
-// same as lua_pcall, except that it automatically supplies 
-// traceback_coroutine as a message handler.
+// Similar to lua_pcall, except that it automatically supplies 
+// traceback_coroutine as a message handler.  It also automatically
+// returns any error message.  Returns empty string if there's
+// no error.
 //
-int traceback_pcall(lua_State *L, int narg, int nret);
+eng::string traceback_pcall(lua_State *L, int narg, int nret);
 
 #endif // TRACEBACK_HPP
diff --git a/luprex/core/cpp/util.cpp b/luprex/core/cpp/util.cpp
index baf21132..ccb3df7a 100644
--- a/luprex/core/cpp/util.cpp
+++ b/luprex/core/cpp/util.cpp
@@ -510,10 +510,6 @@ double distance_squared(double x1, double y1, double x2, double y2) {
     return dx*dx + dy*dy;
 }
 
-bool world_type_authoritative(util::WorldType wt) {
-    return (wt == WORLD_TYPE_MASTER) || (wt == WORLD_TYPE_STANDALONE);
-}
-
 LuaSourcePtr make_lua_source(const eng::string &code) {
     LuaSourcePtr result(new LuaSourceVec);
     eng::string fn = "file.lua";
diff --git a/luprex/core/cpp/util.hpp b/luprex/core/cpp/util.hpp
index ff7e9fb7..33e15d28 100644
--- a/luprex/core/cpp/util.hpp
+++ b/luprex/core/cpp/util.hpp
@@ -212,9 +212,6 @@ eng::string toupper(eng::string input);
 // Calculate distance between two points
 double distance_squared(double x1, double y1, double x2, double y2);
 
-// Return true if a world type is authoritative.
-bool world_type_authoritative(util::WorldType wt);
-
 // Make a LuaSourceVec with one element, for unit testing.
 LuaSourcePtr make_lua_source(const eng::string &code);
 
diff --git a/luprex/core/cpp/world-accessor.cpp b/luprex/core/cpp/world-accessor.cpp
index 7f58bda7..25436c2c 100644
--- a/luprex/core/cpp/world-accessor.cpp
+++ b/luprex/core/cpp/world-accessor.cpp
@@ -294,23 +294,40 @@ LuaDefine(tangible_scan, "plane,x,y,radius,omit_nowhere",
 
 LuaDefine(wait, "nticks",
     "|Wait the specified number of ticks.") {
-    if ((lua_gettop(L) != 1) || (lua_type(L, -1) != LUA_TNUMBER)) {
-        luaL_error(L, "Argument to wait must be a number.");
+    World *w = World::fetch_global_pointer(L);
+    LuaArg seconds;
+    LuaStack LS(L, seconds);
+    int64_t n = LS.ckinteger(seconds);
+    if ((n < 0) || (n > 1000000)) {
+        luaL_error(L, "Argument to wait must be between 0 and 1000000");
+        return LS.result();
+    }
+    if (!lua_isyieldable(L)) {
+        // in a probe, wait throws an error.
+        luaL_error(L, "cannot wait in a probe.");
+        return LS.result();
+    } else if (!w->is_authoritative()) {
+        // in a nonauth model, yield is converted to nopredict.
+        lua_yield(L, 0);
+        return LS.result();
+    } else {
+        // in an authoritative model, wait schedules a continuation.
+        w->thread_sched_.add(w->clock_ + n, w->lthread_thread_id_, w->lthread_place_id_);
+        lua_yield(L, 0);
+        return LS.result();
     }
-    return lua_yield(L, 1);
 }
 
-LuaDefine(tangible_nopredict, "",
+LuaDefine(nopredict, "",
     "|Stop predictive execution of this thread.") {
     if (lua_gettop(L) != 0) {
         luaL_error(L, "tangible.nopredict takes no arguments");
     }
     World *w = World::fetch_global_pointer(L);
-    if (util::world_type_authoritative(w->world_type_)) {
-        return 0;
-    } else {
+    if (lua_isyieldable(L) && !w->is_authoritative()) {
         return lua_yield(L, 0);
     }
+    return 0;
 }
 
 LuaDefine(math_random, "(args...)",
diff --git a/luprex/core/cpp/world-core.cpp b/luprex/core/cpp/world-core.cpp
index 149e25ca..e53d206f 100644
--- a/luprex/core/cpp/world-core.cpp
+++ b/luprex/core/cpp/world-core.cpp
@@ -64,7 +64,7 @@ World::World(util::WorldType wt) {
     LS.rawset(LuaRegistry, "tangibles", LuaNewTable);
 
     // Create the globaldb and oncedb in the registry.
-    if (util::world_type_authoritative(wt)) {
+    if ((wt == util::WORLD_TYPE_MASTER) || (wt == util::WORLD_TYPE_STANDALONE)) {
         LS.rawset(LuaRegistry, "globaldb", LuaNewTable);
         LS.rawset(LuaRegistry, "oncedb", LuaNewTable);
     }
@@ -291,23 +291,20 @@ eng::string World::probe_lua(int64_t actor_id, const eng::string &lua) {
     // Call the closure.
     int top = lua_gettop(L);
     lua_pushvalue(L, closure.index());
-    open_lthread_state(actor_id, actor_id, false, true);
-    status = traceback_pcall(L, 0, LUA_MULTRET);
+    open_lthread_state(actor_id, actor_id, 0, false, true);
+    eng::string msg = traceback_pcall(L, 0, LUA_MULTRET);
     
     // If there's an error message, print it.
     // Otherwise, pretty-print the results.
     std::ostream *ostream = lthread_print_stream();
-    if (status == LUA_OK) {
+    if (msg.empty()) {
         for (int i = top + 1; i <= lua_gettop(L); i++) {
             LuaSpecial root(i);
             pprint(LS, root, true, ostream);
             (*ostream) << std::endl;
         }
     } else {
-        const char *msg = lua_tostring(L, -1);
-        if (msg == NULL) {
-            msg = "(error object is not a string)";
-        }
+        assert(msg != "attempt to yield from outside a coroutine");
         (*ostream) << msg << std::endl;
     }
 
@@ -363,13 +360,14 @@ void World::update_gui(int64_t actor_id, int64_t place_id, Gui *gui) {
     lua_pushvalue(L, actor.index());
     lua_pushvalue(L, place.index());
     Gui::store_global_pointer(L, gui);
-    open_lthread_state(actor_id, place_id, false, false);
-    int status = traceback_pcall(L, 2, 0);
+    open_lthread_state(actor_id, place_id, 0, false, false);
+    eng::string msg = traceback_pcall(L, 2, 0);
     close_lthread_state();
     Gui::store_global_pointer(L, nullptr);
-    if (status != 0) {
+    if (!msg.empty()) {
         gui->clear(0);
-        std::cerr << lua_tostring(L, -1);
+        assert(msg != "attempt to yield from outside a coroutine");
+        std::cerr << msg << std::endl;
         LS.result();
         return;
     }
@@ -503,7 +501,7 @@ void World::invoke_lua(int64_t actor_id, int64_t place_id, const eng::string &ac
     LS.newtable(thinfo);
     LS.rawset(thinfo, "thread", thread);
     LS.rawset(thinfo, "actorid", actor_id);
-    LS.rawset(thinfo, "nargs", 0);
+    LS.rawset(thinfo, "isnew", true);
     LS.rawset(thinfo, "useppool", true);
     LS.rawset(thinfo, "print", true);
     
@@ -596,7 +594,7 @@ void World::invoke_plan(int64_t actor_id, int64_t place_id, const eng::string &a
     LS.newtable(thinfo);
     LS.rawset(thinfo, "thread", thread);
     LS.rawset(thinfo, "actorid", actor_id);
-    LS.rawset(thinfo, "nargs", 3); // actor, place, invdata
+    LS.rawset(thinfo, "isnew", true);
     LS.rawset(thinfo, "useppool", true);
     LS.rawset(thinfo, "print", false);
     
@@ -617,7 +615,7 @@ void World::invoke_plan(int64_t actor_id, int64_t place_id, const eng::string &a
 }
 
 void World::invoke_tick(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
-    if (!util::world_type_authoritative(world_type_)) {
+    if (!is_authoritative()) {
         return;
     }
     clock_ += 1;
@@ -625,7 +623,7 @@ void World::invoke_tick(int64_t actor_id, int64_t place_id, const eng::string &a
 }
 
 void World::invoke_lua_source(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
-    if (!util::world_type_authoritative(world_type_)) {
+    if (!is_authoritative()) {
         return;
     }
     // We need some kind of authentication here.
@@ -642,8 +640,8 @@ void World::invoke_lua_source(int64_t actor_id, int64_t place_id, const eng::str
 void World::run_scheduled_threads() {
     assert(stack_is_clear());
     lua_State *L = state();
-    LuaVar tangibles, place, mt, threads, thinfo, actorid, nargs, useppool, thread, print;
-    LuaStack LS(L, tangibles, place, mt, threads, thinfo, actorid, nargs, useppool, thread, print);
+    LuaVar tangibles, place, mt, threads, thinfo, actorid, isnew, useppool, thread, print;
+    LuaStack LS(L, tangibles, place, mt, threads, thinfo, actorid, isnew, useppool, thread, print);
 
     LS.rawget(tangibles, LuaRegistry, "tangibles");
     while (thread_sched_.ready(clock_)) {
@@ -668,8 +666,8 @@ void World::run_scheduled_threads() {
         if (!LS.isnumber(actorid)) {
             continue;
         }
-        LS.rawget(nargs, thinfo, "nargs");
-        if (!LS.isnumber(nargs)) {
+        LS.rawget(isnew, thinfo, "isnew");
+        if (!LS.isboolean(isnew)) {
             continue;
         }
         LS.rawget(useppool, thinfo, "useppool");
@@ -683,35 +681,16 @@ void World::run_scheduled_threads() {
 
         // Resume the coroutine.
         lua_State *CO = LS.ckthread(thread);
-        open_lthread_state(LS.ckinteger(actorid), sched.place_id(), LS.ckboolean(useppool), true);
-        int status = lua_resume(CO, nullptr, LS.ckint(nargs));
+        open_lthread_state(LS.ckinteger(actorid), sched.place_id(), sched.thread_id(), LS.ckboolean(useppool), true);
+        int nargs = LS.ckboolean(isnew) ? (lua_gettop(CO) - 1) : lua_gettop(CO);
+        int status = lua_resume(CO, nullptr, nargs);
         std::ostream *ostream = lthread_print_stream();
 
-        // Three possible outcomes: finished, yielded, or errored.
-        if (!util::world_type_authoritative(world_type_)) {
-            LS.rawset(threads, sched.thread_id(), LuaNil);
-        } else if (status == LUA_YIELD) {
-            // If there's nothing on the stack, infer that tangible.nopredict yielded.
-            if (lua_gettop(CO) == 0) {
-                LS.rawset(threads, sched.thread_id(), LuaNil);
-            }
-            // If there's a single number on the stack, infer that 'wait' yielded.
-            else if ((lua_gettop(CO) == 1) && (lua_isnumber(CO, 1))) {
-                lua_Number delay = lua_tonumber(CO, 1);
-                lua_settop(CO, 0);
-                LS.rawset(thinfo, "nargs", 0);
-                LS.rawset(thinfo, "useppool", false);
-                thread_sched_.add(clock_ + int64_t(delay), sched.thread_id(), sched.place_id());
-            }
-            // In any other case, generate an error and kill the coroutine.
-            else {
-                std::cerr << "Thread yielded incorrectly.  Killing it." << std::endl;
-                LS.rawset(threads, sched.thread_id(), LuaNil);
-            }
-        } else if (status == LUA_OK) {
+        if (status == LUA_OK) {
             // Successfully ran to completion.  Print any return values.
             // Remove from thread table.
             LS.rawget(print, thinfo, "print");
+            LS.rawset(threads, sched.thread_id(), LuaNil);
             LuaStack LSCO(CO);
             if (LS.ckboolean(print)) {
                 for (int i = 1; i <= lua_gettop(CO); i++) {
@@ -719,12 +698,21 @@ void World::run_scheduled_threads() {
                     (*ostream) << std::endl;
                 }
             }
-            LS.rawset(threads, sched.thread_id(), LuaNil);
+        } else if (status == LUA_YIELD) {
+            if (is_authoritative()) {
+                LS.rawset(thinfo, "isnew", false);
+                LS.rawset(thinfo, "useppool", false);
+            } else {
+                // In a nonauth model, a yield is converted to a 'nopredict'.
+                LS.rawset(threads, sched.thread_id(), LuaNil);
+            }
         } else {
             // Generated an error.  Add a traceback, print, and kill the coroutine.
             // Currently, the error is sent to the actor.  That seems... not right in the long run.
-            traceback_coroutine(CO);
-            (*ostream) << lua_tostring(CO, -1);
+            if (is_authoritative()) {
+                traceback_coroutine(CO);
+                (*ostream) << lua_tostring(CO, -1);
+            }
             LS.rawset(threads, sched.thread_id(), LuaNil);
         }
         close_lthread_state();
@@ -757,12 +745,14 @@ void World::clear_lthread_state() {
     lthread_prints_.reset();
     lthread_actor_id_ = 0;
     lthread_place_id_ = 0;
+    lthread_thread_id_ = 0;
     lthread_use_ppool_ = false;
 }
 
-void World::open_lthread_state(int64_t actor, int64_t place, bool ppool, bool prints) {
+void World::open_lthread_state(int64_t actor, int64_t place, int64_t thread, bool ppool, bool prints) {
     lthread_actor_id_ = actor;
     lthread_place_id_ = place;
+    lthread_thread_id_ = thread;
     lthread_use_ppool_ = ppool;
     if (prints) {
         lthread_prints_.reset(new eng::ostringstream);
@@ -780,8 +770,7 @@ void World::close_lthread_state() {
         const eng::string &output = lthread_prints_->str();
         Tangible *actor = tangible_get(lthread_actor_id_);
         if (actor != nullptr) {
-            bool auth = util::world_type_authoritative(world_type_);
-            actor->print_buffer_.add_string(output, auth);
+            actor->print_buffer_.add_string(output, is_authoritative());
         }
     }
     // Now clean up everything.
diff --git a/luprex/core/cpp/world.hpp b/luprex/core/cpp/world.hpp
index d9c64c7a..8a9a1fbd 100644
--- a/luprex/core/cpp/world.hpp
+++ b/luprex/core/cpp/world.hpp
@@ -212,6 +212,10 @@ public:
     //
     static World *fetch_global_pointer(lua_State *L);
 
+    // Check if the world is authoritative.
+    //
+    bool is_authoritative() const { return (world_type_ == util::WORLD_TYPE_MASTER) || (world_type_ == util::WORLD_TYPE_STANDALONE); }
+
     // Serialize and deserialize.
     //
     void serialize(StreamBuffer *sb);
@@ -245,7 +249,7 @@ public:
     // cleared.
     //
     void clear_lthread_state();
-    void open_lthread_state(int64_t actor_id, int64_t place_id, bool ppool, bool prints);
+    void open_lthread_state(int64_t actor_id, int64_t place_id, int64_t thread_id, bool ppool, bool prints);
     void close_lthread_state();
 
     std::ostream *lthread_print_stream() const;
@@ -260,7 +264,6 @@ public:
     int64_t alloc_id_predictable();
     
 private:
-
     // Store a pointer to a world model into a lua registry.
     //
     static void store_global_pointer(lua_State *L, World *w);
@@ -489,6 +492,7 @@ private:
     //
     int64_t lthread_actor_id_;
     int64_t lthread_place_id_;
+    int64_t lthread_thread_id_;
     int64_t lthread_use_ppool_;
     std::unique_ptr<eng::ostringstream> lthread_prints_;
 
@@ -503,6 +507,8 @@ private:
     friend int lfn_tangible_scan(lua_State *L);
     friend int lfn_math_random(lua_State *L);
     friend int lfn_math_randomstate(lua_State *L);
+    friend int lfn_wait(lua_State *L);
+    friend int lfn_nopredict(lua_State *L);
 };
 
 using UniqueWorld = std::unique_ptr<World>;
diff --git a/luprex/core/lua/login.lua b/luprex/core/lua/login.lua
index 08180efa..04b9bd0a 100644
--- a/luprex/core/lua/login.lua
+++ b/luprex/core/lua/login.lua
@@ -3,6 +3,7 @@ makeclass('login')
 function login.interface(actor, place)
     gui.menu_item("cb_becomeplayer", "Become a Player")
     gui.menu_item("cb_p123", "Print 1, 2, 3")
+    gui.menu_item("cb_p123_nopredict", "Print 1, 2, 3 nopredict")
     end
 
 function login.cb_becomeplayer(actor, place, dialog)
@@ -20,9 +21,21 @@ function login.cb_p123(actor, place, dialog)
     print(3)
     end
 
+function login.cb_p123_nopredict(actor, place, dialog)
+    nopredict()
+    print(1)
+    wait(1)
+    print(2)
+    wait(1)
+    print(3)
+    end
+
 -- this is function documentation for setfoo.
 function setfoo(n)
-    tangible.nopredict()
+    if (n == nil) then 
+        error("setfoo(n) - n must be an integer")
+    end
+    nopredict()
     tangible.actor().inventory.foo = n
     end
 
diff --git a/luprex/eris-master/src/ldo.c b/luprex/eris-master/src/ldo.c
index e9dd5fa9..1117d8f4 100644
--- a/luprex/eris-master/src/ldo.c
+++ b/luprex/eris-master/src/ldo.c
@@ -591,6 +591,9 @@ LUA_API int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k) {
   return 0;  /* return to 'luaD_hook' */
 }
 
+LUA_API int lua_isyieldable (lua_State *L) {
+  return (L->nny == 0);
+}
 
 int luaD_pcall (lua_State *L, Pfunc func, void *u,
                 ptrdiff_t old_top, ptrdiff_t ef) {
diff --git a/luprex/eris-master/src/lua.h b/luprex/eris-master/src/lua.h
index a78a5e1b..165d685d 100644
--- a/luprex/eris-master/src/lua.h
+++ b/luprex/eris-master/src/lua.h
@@ -277,6 +277,7 @@ LUA_API int  (lua_yieldk) (lua_State *L, int nresults, int ctx,
 #define lua_yield(L,n)		lua_yieldk(L, (n), 0, NULL)
 LUA_API int  (lua_resume) (lua_State *L, lua_State *from, int narg);
 LUA_API int  (lua_status) (lua_State *L);
+LUA_API int  (lua_isyieldable) (lua_State *L);
 
 /*
 ** garbage-collection function and options