00:00 Union types play a very big role in Elm's core libraries. A very common union type to use is boolean. The boolean type is just defined like this, and this is it. There's nothing special about booleans. It's not a primitive type. It's just a union type that has the two possible values, true or false.
00:20 As a result, we can use booleans, for example, in pattern matching expressions. For example, if I wanted to have a render function from bool to string, so render would take a boolean, and then it could return, if the boolean is true, the string yep, and if it's false, then nah.
00:46 Let me just comment this out so it doesn't conflict with existing bool type, and I could now change the main function to instead display a render for true. You could see that this compiles and renders yep as expected.