Don't list empty fields

spectec/src/backend-prose/print.ml

@@ -57,10 +57,18 @@ let rec string_of_iter = function
 (* Expressions *)
 
 and string_of_record_expr r =
-  Util.Record.fold
-    (fun a v acc -> acc ^ string_of_atom a ^ ": " ^ string_of_expr v ^ "; ")
-    r "{ "
-  ^ "}"
+  let open Util in
+
+  let record_fields =
+    r
+    |> Record.to_list
+    (* Don't list empty field *)
+    |> List.filter (fun (_, v) -> v.it <> ListE [])
+    |> List.map (fun (a, v) -> string_of_atom a ^ ": " ^ string_of_expr v)
+    |> String.concat "; "
+  in
+
+  if record_fields = "" then "{}" else "{ " ^ record_fields ^ " }"
 
 and string_of_expr expr =
   match expr.it with

spectec/src/backend-prose/render.ml

@@ -351,9 +351,12 @@ and al_to_el_record record =
   Util.Record.fold
     (fun a e expfield ->
       let* expfield = expfield in
-      let* ele = al_to_el_expr e in
-      let elelem = El.Ast.Elem (a, ele) in
-      Some (expfield @ [ elelem ]))
+      (* Don't list empty field *)
+      if e.it = Al.Ast.ListE [] then Some (expfield)
+      else
+        let* ele = al_to_el_expr e in
+        let elelem = El.Ast.Elem (a, ele) in
+        Some (expfield @ [ elelem ]))
     record (Some [])