diff -r 47272fac86d8 -r b287510a4202 src/HOL/Data_Structures/Define_Time_0.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Data_Structures/Define_Time_0.ML	Mon Jan 15 22:50:13 2024 +0100
@@ -0,0 +1,43 @@
+signature ZERO_FUNCS =
+sig
+
+val is_zero : theory -> string * typ -> bool
+
+end
+
+structure Zero_Funcs : ZERO_FUNCS =
+struct
+
+fun get_constrs thy (Type (n, _)) = these (Ctr_Sugar.ctr_sugar_of_global thy n |> Option.map #ctrs)
+  | get_constrs _ _ = []
+(* returns if something is a constructor (found in smt_normalize.ML) *)
+fun is_constr thy (n, T) =
+    let fun match (Const (m, U)) = m = n andalso Sign.typ_instance thy (T, U)
+          | match _ = error "Internal error: unknown constructor"
+    in can (the o find_first match o get_constrs thy o Term.body_type) T end
+
+
+structure ZeroFuns = Theory_Data(
+  type T = Symtab.set
+  val empty = Symtab.empty
+  val merge = Symtab.merge (K true));
+
+fun add_zero f = ZeroFuns.map (Symtab.insert_set f);
+fun is_zero_decl lthy f = Option.isSome ((Symtab.lookup o ZeroFuns.get) lthy f);
+(* Zero should be everything which is a constructor or something like a constant or variable *)
+fun is_zero ctxt (n, (T as Type (Tn,_))) = (Tn <> "fun" orelse is_constr ctxt (n, T) orelse is_zero_decl ctxt n)
+  | is_zero _ _  = false
+
+fun save func thy =
+let
+val fterm = Syntax.read_term (Proof_Context.init_global thy) func;
+val name = (case fterm of Const (n,_) => n | _ => raise Fail "Invalid function")
+val _ = writeln ("Adding \"" ^ name ^ "\" to 0 functions")
+in add_zero name thy
+end
+
+val _ =
+  Outer_Syntax.command \<^command_keyword>\<open>define_time_0\<close> "ML setup for global theory"
+    (Parse.prop >> (Toplevel.theory o save));
+
+end
\ No newline at end of file