fix: do nothing

pta2maude/src/Parser.py

@@ -1031,7 +1031,7 @@ class InterpreterParser(Parser):
         updates = " ; ".join(
             [re.sub(r"(\S+)\s*:=\s*(\S+)", r"\1 := \2", u) for u in t.update]
         )
-        updates_str = "" if (updates == "") else f" do {{ {updates} }}"
+        updates_str = "nothing" if updates == "" else updates
 
         # sync
         actions = t.sync
@@ -1040,7 +1040,7 @@ class InterpreterParser(Parser):
         # guard
         guard = self._normalize_constraints(t.guard)
 
-        return f"when {guard} {sync_str}{updates_str} goto {t.target}"
+        return f"when {guard} {sync_str} do {{ {updates_str} }} goto {t.target}"
 
     def _get_automaton(self, automaton: Automaton, sync_actions: list[str]) -> str:
         """Get the encoding of an automaton in the Maude interpreter