'in'关键字在F#中有什么作用？

let checkNumber n =
    match n with
    | 0 -> "Zero"
    | 1 -> "One"
    | _ -> "Other"

let result = checkNumber 2 // result = "Other"

let numbers = [1; 2; 3; 4; 5]
let squaredNumbers = [for n in numbers -> n * n] // squaredNumbers = [1; 4; 9; 16; 25]