1 # compare mutable.mu
 2 
 3 def main [
 4   local-scope
 5   x:&:num <- new number:type
 6   foo x
 7 ]
 8 
 9 def foo x:&:num [
10   local-scope
11   load-inputs
12   *x <- copy 34  # will cause an error because x is immutable in this function
13 ]