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>

let [<Literal>] 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
        // If the JSON schema changes, this will fail compilation
        printfn "ID %i, USER: %i, TITLE %s, COMPLETED %b"
            todo.id
            todo.userId
            todo.title
            todo.completed
}