types.md

Types

We may want to add incremental typing via interfaces. They are different from variables by starting with an upper case name.

Interfaces

The value types can be combined into interfaces:

User = { id:Number, name:Text }
ListOfNumbers = [Number]
ListOfUsers = [User]
HashOfNumbers = <Number>
HashOfUsers = <User>

Handlers, Templates and Functions can specify the interfaces that they expect. Code that calls them must pass in values that conform to the expected interfaces:

drawUser = template(User user) {
	<div class="user">
		"Name: " user.name
	</div>
}
drawUser({ id:1, name:"Marcus" }) // this compiles
drawUser({ name:"Ashley" }) // this won't compile. drawUser expects a User, which has { id:Number } in addition to { name:Text }

The expected interface can be inlined, though it's good practice to explicitly name interfaces. For example, drawUser does not depend on user.id so it could specify a smaller interface:

drawUser2 = template({ name:Text } user) {
	<div class="user">"Name: " user.name</div>
}
drawUser2({ id:1, name:"Marcus" }) // this runs
drawUser2({ name:"Ashley" }) // as does this

Getting the type of a value is simple. This emits "Number":

var a = 1
a.Type

Old example of possible example typed chat app:

#import WebSocket

Message = { body:Text }

var [Message] messages = []

WebSocket.on('message', handler(Message message) { messages.push(message) })

<div class="chat">
	var input = ""
	<input data=input />
	<button>"Send"</button onClick=handler() {
		var message = { body:input.copy() }
		input.set('')
		WebSocket.send('message', message)
		messages.push(message)
	}>
	<div class="messages">
		for (message in messages) {
			<div class="message"> message.body </div>
		}
	</div>
</div>