We discussed polymorphic datatypes, such as SML's built in lists as
well as a user-defined polymorphic tree type.
We wrote several
polymorphic functions, including trav : 'a tree -> 'a
list and zip : 'a list * 'b list -> ('a * 'b)
list.
We discussed the polymorphic 'a option datatype and wrote a polymorphic lookup function.
We discussed how SML infers types of values, including functions.