containers := SM.insert (!containers, name, (befor, after))
fun container name = SM.find (!containers, name)
+val functions : (exp list -> exp option) SM.map ref = ref SM.empty
+fun registerFunction (name, f) =
+ functions := SM.insert (!functions, name, f)
+fun function name = SM.find (!functions, name)
+
local
val pr = ref (fn () => ())
in