DSL EXPRESSION:
$[$y] = 4


AST:
"block" [tt:block] [nt:StatementBlock]
    "=" [tt:equals] [nt:Assignment]
        "$[]" [tt:$[]] [nt:IndirectFieldValue]
            "$y" [tt:field_name] [nt:DirectFieldValue]
        "4" [tt:int_literal] [nt:int_literal]

