Pattern matching is used for control flow and for transforming input data. It allows you to look at a value, test it against a series of conditions, and perform certain computations depending on whether that condition is met.
if ... then statements in other languages.The basic syntax of pattern matching is as follows.
match expr with
| pattern1 -> result1
| pattern2 -> result2
| pattern3 [ when condition ] -> result3
| _ -> defaultResult
| defines a condition.-> means if the condition is true, return this value._ is the default pattern, meaning that it matches anything, sort of like a wildcard.The following example shows the usage of pattern matching.
type Category =
| Sports = 0
| Arts = 1
| Clothing = 2
| Electronics = 3
| HealthCare = 4
let printCategoryName (category:Category) =
match category with
| Category.Sports -> Console.WriteLine("Selected Category: Sports")
| Category.Arts -> Console.WriteLine("Selected Category: Arts")
| Category.Clothing -> Console.WriteLine("Selected Category: Clothing")
| Category.Electronics -> Console.WriteLine("Selected Category: Electronics")
| Category.HealthCare -> Console.WriteLine("Selected Category: HealthCare")
| _ -> ()
printCategoryName Category.Arts
printCategoryName Category.HealthCare
printCategoryName Category.Electronics
You can also chain together multiple conditions which return the same value as shown below.
let greeting name =
match name with
| "Steve" | "Kristina" | "Matt" -> Console.WriteLine("Hello! {0}", name)
| "Carlos" | "Maria" -> Console.WriteLine("Hola! {0}", name)
| "Worf" -> Console.WriteLine("nuqneH! {0}", name)
| "Pierre" | "Monique" -> Console.WriteLine("Bonjour! {0}", name)
| _ -> Console.WriteLine("DOES NOT COMPUTE! {0}", name)
greeting "Monique"
greeting "Kristina"
greeting "Sakura"
It will print the following output on the console.
Bonjour! Monique
Hello! Kristina
DOES NOT COMPUTE! Sakura