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. The call x |=> y gives a finite partial function that maps x to y
and is undefined for all arguments other than x.
EXAMPLE
# let f = (1 |=> 2);;
val f : (int, int) func =
# apply f 1;;
val it : int = 2
# apply f 2;;
Exception: Failure "apply".