module type External =sig..end
External view of the tree, with accessors.
Automatically built by the functor Structure.Open from an Structure.Internal datatype.
When a generic datatype is a combination of several other datatypes, these
functions allow interacting with its subparts. Note that their behavior is
undefined if the overall datatype contains several times the same datatype.
type
type 'a key
val mem : 'a key -> bool
val get : 'a key -> (t -> 'a) option
val set : 'a key ->
'a -> t -> t