This is one of a suite of operations on finite partial functions, type
('a,'b)func. These may sometimes be preferable to ordinary functions since
they permit more operations such as equality comparison, extraction of domain
etc. If f is a finite partial function then (x |-> y) f gives a modified
version that maps x to y (whether or not f was defined on x before and
regardless of the old value) but is otherwise the same.
FAILURE CONDITIONS
Never fails.
EXAMPLE
# let f = (1 |-> 2) undefined;;
val f : (int, int) func =
# let g = (1 |-> 3) f;;
val g : (int, int) func =
# apply f 1;;
val it : int = 2
# apply g 1;;
val it : int = 3