type Face =
    | Ace | King | Queen | Jack
    | Number of int
type Color =
    | Spades | Hearts | Diamonds | Clubs
type Card =
    | Face * Color

let aceOfHearts = Ace,Hearts
let tenOfSpades = (Number 10), Spades

match card with
| Ace, Hearts ->
    printfn "Ace Of Hearts!"
| _, Hearts ->
    printfn "A lovely heart"
| (Number 10), Spades ->
    printfn "10 of Spades"
| _, (Diamonds|Clubs) ->
    printfn "Diamonds or clubs"
// Warning:
// Incomplete pattern matches on this expression.
// For example, the value '(_,Spades)' may indicate
// a case not covered by the pattern(s).

// JS promises made easy
promise {
    let! res = Fetch.fetch url []
    let! txt = res.text()
    return txt.Length
}

// Declare your own computation expression
type OptionBuilder() =
    member __.Bind(opt, binder) =
        match opt with
            | Some value -> binder value
            | None -> None
    member __.Return(value) =
        Some value

let option = OptionBuilder()

option {
    let! x = trySomething()
    let! y = trySomethingElse()
    let! z = andYetTrySomethingElse()
    // Code will only hit this point if the three
    // operations above return Some
    return x + y + z
}

[<Measure>] type m
[<Measure>] type s

let distance = 12.0<m>
let time = 6.0<s>

let thisWillFail = distance + time
// ERROR: The unit of measure 'm' does
// not match the unit of measure 's'

let thisWorks = distance / time
// 2.0<m/s>

[<Literal>]
let JSON_URL = "https://jsonplaceholder.typicode.com/todos"

// Type is created automatically from the url
type Todos = Fable.JsonProvider.Generator<JSON_URL>

async {
    let! (_, res) = Fable.SimpleHttp.Http.get url
    let todos = Todos.ParseArray res
    for todo in todos do
        // Compilation fail if the JSON schema changes
        printfn "ID %i, USER: %i, TITLE %s, COMPLETED %b"
            todo.id
            todo.userId
            todo.title
            todo.completed
}