exit status: 1 with stderr:
<stdin>:6:15: error: immutable value 'l' may only be initialized once async let (l, r) = (left(), right()) ^ <stdin>:6:20: note: initial value already provided in 'let' declaration async let (l, r) = (left(), right()) ^ <stdin>:6:15: note: change 'let' to 'var' to make it mutable async let (l, r) = (left(), right()) ^~~ var <stdin>:6:15: error: immutable value 'r' may only be initialized once async let (l, r) = (left(), right()) ^ <stdin>:6:23: note: initial value already provided in 'let' declaration async let (l, r) = (left(), right()) ^ <stdin>:6:15: note: change 'let' to 'var' to make it mutable async let (l, r) = (left(), right()) ^~~ var