Type inference (example)

wrap(str, width) =
    all = [] ; line = ""
    str.words.each.(l ->
        if size(line+l) >= width then
            all += [line]
            line = ""
        line += (line &&& " ") + l
    )
    join(all + [line], "\n")

str.words    implies    str !< String
                 since  words !! String -> [String]
size(...) >= width    implies    width !< Uint
                 since  size !! Enumerable(a) -> Uint
the return value join(...) !! String
                 since  join !! o(a), a -> o !< Vector ; a !< Addable ; a

 The result is:    wrap !! String, Uint -> String
⇒  each call to wrap will be type-checked
       wrap("foo", "bar")    is ill-typed and is rejected