As the pattern matches contain more and more rules, you might want to combine patterns. There are two ways to combine patterns. First is to use OR represented by a
vertical pipe | , which combines patterns together so the rule will fire if any of the grouped patterns match. Second is to use AND represented by an ampersand &, which combines patterns together so that the rule will fire only if all of the grouped patterns match.
let vowelTest c =
match c with
let describeNumbers x y =
match x,y with
| 1, _
| _, 1
-> "One of the numbers is one."
| (2,_) & (_,2)
-> "Both of the numbers is two."
AND pattern has litte use in normal pattern matching, however itz invaluable when using active patterns.