Between Active Pattern

between.fsx

open System

[<return:Struct>]
let inline (|Between|_|) left right value =
    if value > left && value < right then ValueSome () else ValueNone

let today = DateTime.Now
let yesterday = DateTime.Now.AddDays(-1.0)
let tomorrow = DateTime.Now.AddDays(1.0)
let twoDaysAgo = DateTime.Now.AddDays(-2.0)

match today with
| Between twoDaysAgo yesterday -> printfn "Today is between two days ago and yesterday"
| Between yesterday tomorrow -> printfn "Today is between yesterday and tomorrow"
| _ -> printfn "Today is not between yesterday and tomorrow"


match 10 with
| Between 0 5 -> "too far..."
| Between 5 10 -> "closer..."
| Between 10 15 -> "got it"
| _ -> "Impossible to tell :("