Lang: Syntax error with with unbox operator

[phated]

This program doesn't parse:

data Container = {
    size: Box<Number>
}

let make = () => {
    { size: box(1) }
}

let getSize= (m) => {
  let size = ^m.size;
  size
}

let a = make();
print(getSize(a));

It gives this error:

$ grain test.gr 
File "test.gr", line 1, characters 0-0:
Error: The Grain compiler had trouble parsing your program.