F# Pattern Matching

F# provides pattern matching to match data logically. It is similar to nested if else and switch cases used in C, C++ programming languages. We can apply pattern matching on caonstant values, objects, lists, records, etc.

F# Pattern Matching on Constant Values Example

You can use constant values in pattern matching like given following example.

let patternMatch a = 
 match a with
  | 1 -> "You entered 1"
  | 2 -> "You entered 2"
  | _ -> "You entered something other then 1 or 2"

printf "%s" (patternMatch 2)

Output:

You entered 2

F# Pattern Matching using Object Example

You can use objects in pattern to search best match of your input.

let objectPatternMatch (a:obj) = 
 match a with 
 | :? int -> "You entered integer value"
 | :? float -> "You entered float value"
 | _ -> "You entered something other than integer or float"

printfn "%s" (objectPatternMatch 10)

Output:

You entered integer value

F# Conditional Pattern Matching Example

Following program shows how to use condinal pattern matching.

let conditionalPatternMatching x y = 
 match (x,y) with
  | (x,y) when x>y -> printfn "X is greater than y"
  | (x,y) when x<y -> printfn "Y is greater than x"
  | _ -> printf "X = Y"

conditionalPatternMatching 20 10

Output:

X is greater than y

F# Pattern Matching in list

In F#, you can apply pattern matching in list. Let's see an example.

let listPatternMatching list = 
 match list with
  | [var] -> var
  | [var1;var2]-> var1+var2

printf "%d" (listPatternMatching [2;1])

Output:

F# Pattern Matching in Tuples

You can use pattern matching in tuples also. Let's see an example.

let tuplePatternMatching tuple =
    match tuple with
    | (0, 0) -> printfn "Both values zero."
    | (0, var2) -> printfn "First value is 0 in (0, %d)" var2
    | (var1, 0) -> printfn "Second value is 0 in (%d, 0)" var1
    | _ -> printfn "Both nonzero."
tuplePatternMatching (0, 1)

Output: