ometa joy {
     number = digit+:n -> parseInt(n.join('')),
     symbol = '+'
            | '-',
     list = '[' nextWord*:n space* ']' -> n,
     nextWord = space* (number | symbol | list),
     
     toplevel = nextWord*:l space* end -> l
     } 

tree = joy.matchAll("2 3[4 5]+", "toplevel")

alert(tree)