Is there a decompiler available that produces something that looks like source code from bytecode vectors?
Not that I'm aware of, but it shouldn't be too hard to make one, except for possible indentation being lost. And perhaps parenthesis (I like putting in a few redundant ones to make my code easier to read).
If you use Mango to parse source, you get parse trees which can be "unparsed" back into source form. The unparsing is an exact inverse of parsing, preserving indentation etc.