diff --git a/hosts/ocaml/bin/sx_server.ml b/hosts/ocaml/bin/sx_server.ml
index 6fa25ec..cbdd77f 100644
--- a/hosts/ocaml/bin/sx_server.ml
+++ b/hosts/ocaml/bin/sx_server.ml
@@ -593,14 +593,17 @@ let make_server_env () =
   bind "primitive?" (fun args ->
     match args with
     | [String name] ->
-      (* Check if name is bound in the env as a NativeFn *)
-      (try match env_get env name with NativeFn _ -> Bool true | _ -> Bool false
-       with _ -> Bool false)
+      (* Check both the primitives table and the env *)
+      Bool (Sx_primitives.is_primitive name ||
+            (try (match env_get env name with NativeFn _ -> true | _ -> false)
+             with _ -> false))
     | _ -> Bool false);
   bind "get-primitive" (fun args ->
     match args with
     | [String name] ->
-      (try env_get env name with _ -> Nil)
+      (* Check primitives table first, then env *)
+      (try Sx_primitives.get_primitive name
+       with _ -> try env_get env name with _ -> Nil)
     | _ -> Nil);
 
   (* Character classification — platform primitives for spec/parser.sx *)
diff --git a/hosts/ocaml/lib/sx_primitives.ml b/hosts/ocaml/lib/sx_primitives.ml
index f821212..3eb3c52 100644
--- a/hosts/ocaml/lib/sx_primitives.ml
+++ b/hosts/ocaml/lib/sx_primitives.ml
@@ -283,8 +283,17 @@ let () =
       String (String.concat sep (List.map to_string items))
     | _ -> raise (Eval_error "join: 2 args"));
   register "replace" (fun args ->
+    let to_str = function
+      | String s -> s | SxExpr s -> s | RawHTML s -> s
+      | Keyword k -> k | Symbol s -> s
+      | Nil -> "" | Bool true -> "true" | Bool false -> "false"
+      | Number n -> if Float.is_integer n then string_of_int (int_of_float n) else Printf.sprintf "%g" n
+      | Thunk _ as t -> (match !_sx_trampoline_fn t with String s -> s | v -> to_string v)
+      | v -> to_string v
+    in
     match args with
-    | [String s; String old_s; String new_s] ->
+    | [s; old_s; new_s] ->
+      let s = to_str s and old_s = to_str old_s and new_s = to_str new_s in
       let ol = String.length old_s in
       if ol = 0 then String s
       else begin