Default function argument values

[kengorab]

Related to #23, this is the ability for functions to have default parameter values

func myAdd(a: Int, b: Int, c: Int = 0) = a + b + c

func myAdd2(a: Int, b: Int, c = 0) {
  val sum = a + b + c
  sum
}

Implementation notes:

Let's say we have this function:

func abc(a: Int, b = 1, c = "hello"): String = a + b + c

Behind the scenes, the following code will be generated:

func abc_$1(a: Int) = abc(a, 1, "hello")
func abc_$2(a: Int, b: Int) = abc(a, b, "hello")

(the _$2 means "the version of the abc function, with arity 2). Those 2 parameters would be forwarded to the underlying function, with the 3rd param receiving its default value of "hello".

This means that the logic for invocation also needs to be aware of these "pesudo-functions"