Validation with exceptions

ExceptionValidation.fs

module private Assert =
    let validName name = if System.String.IsNullOrEmpty(name) then invalidArg "name" "The name must not be null." else name
    let validCount count = if count <= 0 then invalidArg "count" "Inventory count must be positive." else count
    let inactive item = if item.isActive = true then failwith "The item is already deactivated."
 
let exec item = 
    let apply event = 
        let newItem = apply item event
        event
    function
    | Create(name)        -> name |> Assert.validName |> Created |> apply                    
    | Deactivate          -> item |> Assert.inactive; Deactivated |> apply        
    | Rename(name)        -> name |> Assert.validName |> Renamed |> apply        
    | CheckInItems(count) -> count |> Assert.validCount |> ItemsCheckedIn |> apply        
    | RemoveItems(count)  -> count |> Assert.validCount |> ItemsRemoved |> apply