https://github.com/akkartik/mu/blob/master/apps/ex2.2.mu
 1 fn main -> result/ebx: int {
 2   result <- foo
 3 }
 4 
 5 fn foo -> result/ebx: int {
 6   var n: int
 7   copy-to n, 3
 8   increment n
 9   result <- copy n
10 }