How to directly apply a function to the value of a match expression in F#

Question

Assuming I have

let someFunction someVar =
  let x = 
    match someVar with
    | Value1 -> 10
    | Value2 -> 20
  anotherFunction x

Is there a way to directly apply "anotherFunction" to the return of the match expression without using the auxiliary "x" variable?

Answer 1

Yes, you can just apply it directly.

let someFunction someVar =
    anotherFunction( 
        match someVar with
        | Value1 -> 10
        | Value2 -> 20)

Like most other things in F#, match blocks are expressions that you can use inline if you think it improves your code. I'm not convinced it's preferable in this case though.

Answer 2

If the name of someVar is not important you can use function composition as a way to express the function:

let someFunction =
    function
    | Value1 -> 10
    | Value2 -> 20
    >> anotherFunction

The function keyword is syntactic sugar for fun x -> match x with... The >> operator takes a function and applies it to another function.

Answer 3

The existing answers show you how to do what you want, but if I was writing the code, I would just repeat the function call inside the match - I prefer that because it is placing "small expression" (function call) inside a "large expression" (pattern matching). The other way round, you end up with a large expression inside a small one, which makes the syntax less clear (in my view).

If you also use function to avoid someVar , it becomes a neat three-liner:

let someFunction = function
  | Value1 -> anotherFunction 10
  | Value2 -> anotherFunction 20