sig
type param =
[ `Builtin of Value_types.call_result | `Def | `Memexec | `Spec ] *
state * callstack
type result = unit
val extend : (param -> result) -> unit
val extend_once : (param -> result) -> unit
val apply : param -> result
val is_empty : unit -> bool
val clear : unit -> unit
val length : unit -> int
end