# This is how you can emulate Python's semantics for default variables.
let l = []
def foo(x=l):
    x.append("more")
    print(x)

foo() # → ['more']
foo() # → ['more', 'more']
foo([1,2]) # → [1, 2, 'more']
foo() # → ['more', 'more', 'more']
foo() # → ['more', 'more', 'more', 'more']
foo(['a', 'b']) # → ['a', 'b', 'more']