Good call. Quote from the PDF in the meantime:

"To give a sense of what programming in Boomerang is like, we will define the lens implementing the transformations between XML and CSV composers shown above.

First we define a lens c that handles a single <composer> element. It uses a number of functions defined in our XML library, as well as primtives for copying (copy) and deleting (del) strings, and for concatenating lenses (.).

    let c : lens =
      Xml.elt NL2 "composer"
        begin
          Xml.simple_elt NL4 "name"
            (copy [A-Za-z ]+ . ins ", ") .
          Xml.attr2_elt_no_kids NL4 "years"
            "birth" (copy NUMBER . ins "-")
            "death" (copy NUMBER) .
          Xml.simple_elt NL4 "nationality" (del [A-Za-z]+)
        end

Using c, we then define a lens that handles a top-level <composers> element, enclosing a list of <composers>. This lens is defined using the features already described, a primitive for inserting a string (ins), as well as union (|) and Kleene star.

    let cs : lens =
      Xml.elt NL0 "composers"
        begin
          copy EPSILON |
          c . (ins newline . c)*
        end

..."