The TABLE interface is similar to the ORD_MAP interface from the SML/NJ Library. It however has several additional features.
First it supplies a generalized update function, generalUpdate, which can be used to implement search, insert or delete as well as many other combinations. For example, it can be used to update the value associated with a key while returning the old value, or conditionally delete a value. These operations would require two operations and hence two searches through the data-structure in a standard purely functional interface (such as ORD_MAP). With the generalUpdate they only require a single search.
There is also a slightly more specific function update that can update the value of a key in the same way as genUpdate, but it will not return a value. This, for example can be used to implement insert as follows:
fun insert(key, value, table) =
update (fn _ => SOME(value)) (key, table)
Alternatively you could define a version that raises an exception
if the item is already in the table:
fun insert(key, value, table) =
update (fn SOME(_) => raise alreadyThereException
| NONE => SOME(value))
(key, table)
As another example,
if you wanted to delete an item if it is in the table but add it if
it is not, you could implement this as:
fun insertDelete(key, value, table) =
update (fn SOME(_) => NONE
| NONE => SOME(value))
(key, table)
Also, in addition to intersect and union, there is a diff function.