diff --git a/luprex/cpp/core/http.cpp b/luprex/cpp/core/http.cpp
index 962a099d..35c6eb83 100644
--- a/luprex/cpp/core/http.cpp
+++ b/luprex/cpp/core/http.cpp
@@ -623,59 +623,66 @@ void HttpClientRequest::set_content(const eng::string &content) {
 }
 
 void HttpClientRequest::set_verify_certificate(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isboolean(val)) {
+    auto tval = LS.tryboolean(val);
+    if (!tval) {
         check_fail(util::ss("verifycertificate must be a boolean"));
         return;
     }
-    set_verify_certificate(LS.ckboolean(val));
+    set_verify_certificate(*tval);
 }
 
 void HttpClientRequest::set_method(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("method must be a string"));
         return;
     }
-    set_method(LS.ckstring(val));
+    set_method(*tval);
 }
 
 void HttpClientRequest::set_host(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("host must be a string"));
         return;
     }
-    set_host(LS.ckstring(val));
+    set_host(*tval);
 }
 
 void HttpClientRequest::set_port(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isint(val)) {
+    auto tval = LS.tryint(val);
+    if (!tval) {
         check_fail(util::ss("port must be an int"));
         return;
     }
-    set_port(LS.ckint(val));
+    set_port(*tval);
 }
 
 void HttpClientRequest::set_path(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("path must be a string"));
         return;
     }
-    set_path(LS.ckstring(val));
+    set_path(*tval);
 }
 
 void HttpClientRequest::set_param(LuaCoreStack &LS, LuaSlot key, LuaSlot val) {
-    if (!LS.isstring(key)) {
+    auto tkey = LS.trystring(key);
+    auto tval = LS.trystring(val);
+    if (!tkey) {
         check_fail(util::ss("url parameter key must be a string"));
         return;
     }
-    if (!LS.isstring(val)) {
+    if (!tval) {
         check_fail(util::ss("url parameter val must be a string"));
         return;
     }
-    set_param(LS.ckstring(key), LS.ckstring(val));
+    set_param(*tkey, *tval);
 }
 
 void HttpClientRequest::set_params(LuaCoreStack &LS0, LuaSlot tab) {
-    if (!LS0.istable(tab)) {
+    if (!LS0.trytable(tab)) {
         check_fail(util::ss("params must be a table"));
         return;
     }
@@ -688,27 +695,30 @@ void HttpClientRequest::set_params(LuaCoreStack &LS0, LuaSlot tab) {
 }
 
 void HttpClientRequest::set_url(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("url must be a string"));
         return;
     }
-    set_url(LS.ckstring(val));
+    set_url(*tval);
 }
 
 void HttpClientRequest::set_mime_type(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("mime type must be a string"));
         return;
     }
-    set_mime_type(LS.ckstring(val));
+    set_mime_type(*tval);
 }
 
 void HttpClientRequest::set_content(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto tval = LS.trystring(val);
+    if (!tval) {
         check_fail(util::ss("content must be a string"));
         return;
     }
-    set_content(LS.ckstring(val));
+    set_content(*tval);
 }
 
 void HttpClientRequest::set_jsonvalue(LuaCoreStack &LS, LuaSlot val) {
@@ -976,15 +986,16 @@ void HttpServerResponse::set_content(const eng::string &content) {
 
 void HttpServerResponse::set_status(LuaCoreStack &LS, LuaSlot val) {
     int status = 0;
-    if (LS.isstring(val)) {
-        eng::string s = LS.ckstring(val);
-        status = status_code_from_string(s);
+    auto vstring = LS.trystring(val);
+    auto vint = LS.tryint(val);
+    if (vstring) {
+        status = status_code_from_string(*vstring);
         if (status == 0) {
-            check_fail(util::ss("unrecognized status code: ", s));
+            check_fail(util::ss("unrecognized status code: ", *vstring));
             return;
         }
-    } else if (LS.isint(val)) {
-        status = LS.ckint(val);
+    } else if (vint) {
+        status = *vint;
     } else {
         check_fail(util::ss("status must be an integer"));
         return;
@@ -993,27 +1004,30 @@ void HttpServerResponse::set_status(LuaCoreStack &LS, LuaSlot val) {
 }
 
 void HttpServerResponse::set_max_age(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isint(val)) {
+    auto vint = LS.tryint(val);
+    if (!vint) {
         check_fail(util::ss("max-age must be an int"));
         return;
     }
-    set_max_age(LS.ckint(val));
+    set_max_age(*vint);
 }
 
 void HttpServerResponse::set_mime_type(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto vstring = LS.trystring(val); 
+    if (!vstring) {
         check_fail(util::ss("mime type must be a string"));
         return;
     }
-    set_mime_type(LS.ckstring(val));
+    set_mime_type(*vstring);
 }
 
 void HttpServerResponse::set_content(LuaCoreStack &LS, LuaSlot val) {
-    if (!LS.isstring(val)) {
+    auto vstring = LS.trystring(val);
+    if (!vstring) {
         check_fail(util::ss("content must be a string"));
         return;
     }
-    set_content(LS.ckstring(val));
+    set_content(*vstring);
 }
 
 void HttpServerResponse::set_jsonvalue(LuaCoreStack &LS, LuaSlot val) {
diff --git a/luprex/cpp/core/pprint.cpp b/luprex/cpp/core/pprint.cpp
index e7a838d9..73817f02 100644
--- a/luprex/cpp/core/pprint.cpp
+++ b/luprex/cpp/core/pprint.cpp
@@ -120,18 +120,18 @@ public:
         // assign one.
         int tabnum = 0;
         LS.rawget(lchpos, tabchpos_, value);
-        if (!LS.isnumber(lchpos)) {
+        auto chpos = LS.tryint(lchpos);
+        if (!chpos) {
             // First time. Record the character position where the
             // table first appears in the output stream.
             LS.rawset(tabchpos_, value, int((*output_).tellp()));
         } else {
-            int chpos = LS.ckint(lchpos);
-            tabnum = chpos_to_tabnum_[chpos];
+            tabnum = chpos_to_tabnum_[*chpos];
             if (tabnum == 0) {
                 // Second time. The table is already in the output,
                 // but it hasn't been assigned a number.  Assign one.
                 tabnum = next_id_++;
-                chpos_to_tabnum_[chpos] = tabnum;
+                chpos_to_tabnum_[*chpos] = tabnum;
             }
         }
         
diff --git a/luprex/cpp/core/world-difftab.cpp b/luprex/cpp/core/world-difftab.cpp
index ae9e29ae..881ff08f 100644
--- a/luprex/cpp/core/world-difftab.cpp
+++ b/luprex/cpp/core/world-difftab.cpp
@@ -44,20 +44,19 @@ static bool equivalent_values(LuaCoreStack &MLS, LuaSlot mval, LuaSlot mtnmap,
     switch (MLS.xtype(mval)) {
     case LUA_TBOOLEAN: {
         if (SLS.type(sval) != LUA_TBOOLEAN) return false;
-        return MLS.ckboolean(mval) == SLS.ckboolean(sval);
+        return MLS.tryboolean(mval) == SLS.tryboolean(sval);
     }
     case LUA_TNUMBER: {
         if (SLS.type(sval) != LUA_TNUMBER) return false;
-        return MLS.cknumber(mval) == SLS.cknumber(sval);
+        return MLS.trynumber(mval) == SLS.trynumber(sval);
     }
     case LUA_TSTRING: {
-        // This could be faster if I used lua_tolstring directly.
         if (SLS.type(sval) != LUA_TSTRING) return false;
-        return MLS.ckstring(mval) == SLS.ckstring(sval);
+        return MLS.trystring(mval) == SLS.trystring(sval);
     }
     case LUA_TLIGHTUSERDATA: {
         if (SLS.type(sval) != LUA_TLIGHTUSERDATA) return false;
-        return MLS.cktoken(mval) == SLS.cktoken(sval);
+        return MLS.trytoken(mval) == SLS.trytoken(sval);
     }
     case LUA_TFUNCTION: {
         // Cannot really compare.  Just return true if the types match.
@@ -95,22 +94,22 @@ static void transmit_value(LuaCoreStack &MLS, LuaSlot mval, LuaSlot mtnmap, Stre
     switch (MLS.xtype(mval)) {
     case LUA_TBOOLEAN: {
         sb->write_uint8(LUA_TBOOLEAN);
-        sb->write_bool(MLS.ckboolean(mval));
+        sb->write_bool(*MLS.tryboolean(mval));
         return;
     }
     case LUA_TNUMBER: {
         sb->write_uint8(LUA_TNUMBER);
-        sb->write_double(MLS.cknumber(mval));
+        sb->write_double(*MLS.trynumber(mval));
         return;
     }
     case LUA_TSTRING: {
         sb->write_uint8(LUA_TSTRING);
-        sb->write_string(MLS.ckstring(mval));
+        sb->write_string(*MLS.trystring(mval));
         return;
     }
     case LUA_TLIGHTUSERDATA: {
         sb->write_uint8(LUA_TLIGHTUSERDATA);
-        sb->write_uint64(MLS.cktoken(mval).value);
+        sb->write_uint64((*MLS.trytoken(mval)).value);
         return;
     }
     case LUA_TT_GENERAL: {
diff --git a/luprex/cpp/core/world-pairtab.cpp b/luprex/cpp/core/world-pairtab.cpp
index e5210bda..a5b03559 100644
--- a/luprex/cpp/core/world-pairtab.cpp
+++ b/luprex/cpp/core/world-pairtab.cpp
@@ -139,13 +139,13 @@ void World::pair_lua_tables(const IdVector &basis, lua_State *master) {
         if (MLS.isnumber(midx)) continue;
         // If the synch table doesn't have a number, skip.
         SLS.rawget(sidx, stnmap, stab);
-        if (!SLS.isnumber(sidx)) continue;
-        int idx = SLS.ckinteger(sidx);
-        assert((idx >= 1) && (idx <= s_ntables));
+        auto idx = SLS.trynumber(sidx);
+        if (!idx) continue;
+        assert((*idx >= 1) && (*idx <= s_ntables));
         // Pair the tables.
-        MLS.rawset(mtnmap, mtab, idx);
-        MLS.rawset(mntmap, idx, mtab);
-        paired[idx] = true;
+        MLS.rawset(mtnmap, mtab, *idx);
+        MLS.rawset(mntmap, *idx, mtab);
+        paired[*idx] = true;
         // Potentially pair the metatables.
         MLS.getmetatable(mval, mtab);
         if (MLS.istable(mval)) {