Array syntax causes multiple codegen issues in Python

[frame-lang]

This syntax causes python errors.:

    $S0
        |e| [] 
            []
            var x = []
            []
         ^ 
        

Problem 1: empty lists not in an assignment don't generate code:

[]

Additionally this is ambiguous:

        |e| [a] // [a] intended to be a list expression

Explore optional braces around an event handler to separate the parameter list from a list expression:

    $S0
        |e|  {
            [a]
         ^ }