type case simulated using polymorphic sums

bla.hs

foo :: +{ Num : Number, Str : String | r } -> Number
function foo(x) {
    if (typeof x == Number) { .. x is a number here! ...; return 0 }
    else if (typeof x == String) { .. a string here ..; return 1 }
    else { .. }
}

\case x of
   Num n -> ... ; 0
   Str s -> ... ; 1
_ -> ...


addOne :: +{ Num : Number  } -> +{ Num : Number }
function addOne(x) { return x + 1; }

34 :: forall r. +{ Num : Number | r }

'bla' :: forall t. +{ Str : String | t }

foo(34) ===> here instantiated to: foo :: +{ Num : Number, Str : String } -> Number , and 34 :: +{ Num : Number, Str : String }