A format for expressing an ordered list of integers is to use a comma separated list of either

 individual integers
 Or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. (The range includes all integers in the interval including both endpoints)
 The range syntax is to be used only for, and for every range that expands to more than two values.
Example

The list of integers:

 -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20
Is accurately expressed by the range expression:

 -6,-3-1,3-5,7-11,14,15,17-20
(And vice-versa).

Task

 Create a function that takes a list of integers in increasing order and returns a correctly formatted string in the range format. 
 Use the function to compute and print the range formatted version of the following ordered list of integers. (The correct answer is: 0-2,4,6-8,11,12,14-25,27-33,35-39).


    0,  1,  2,  4,  6,  7,  8, 11, 12, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
   25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
   37, 38, 39

 Show the output of your program.


Related task

   Range expansion


function extract_ranges(sequence s)
    integer first
    sequence out
    out = ""
    if length(s) = 0 then
        return out
    end if
    first = 1
    for i = 2 to length(s) do
        if s[i] != s[i-1]+1 then
            if first = i-1 then
                out &= sprintf("%d,", s[first])
            elsif first = i-2 then
                out &= sprintf("%d,%d,", {s[first],s[i-1]})
            else
                out &= sprintf("%d-%d,", {s[first],s[i-1]})
            end if
            first = i
        end if
    end for
    if first = length(s) then
        out &= sprintf("%d", s[first])
    elsif first = length(s)-1 then
        out &= sprintf("%d,%d", {s[first],s[$]})
    else
        out &= sprintf("%d-%d", {s[first],s[$]})
    end if
    return out
end function
 
puts(1, extract_ranges({0, 1, 2, 4, 6, 7, 8, 11, 12, 14, 15, 16, 17, 18, 19,
    20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39}))