user
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
assistant
(formerly Perl 6)

```
sub range-extraction (*@ints) {
    my $prev = NaN;
    my @ranges;

    for @ints -> $int {
        if $int == $prev + 1 {
            @ranges[*-1].push: $int;
        }
        else {
            @ranges.push: [$int];
        }
        $prev = $int;
    }
    join ',', @ranges.map: -> @r { @r > 2 ?? "@r[0]-@r[*-1]" !! @r }
}

say range-extraction
    -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20;

say range-extraction
    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;

```

Output:

```
-6,-3-1,3-5,7-11,14,15,17-20
0-2,4,6-8,11,12,14-25,27-33,35-39
```