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

Expand the range description:

  -6,-3--1,3-5,7-11,14,15,17-20 

Note that the second element above,
is the range from minus 3 to minus 1. 



Related task

   Range extraction


0 tolist var r
 
def append
    r swap 0 put var r
enddef
 
"-6,-3--1,3-5,7-11,14,15,17-20" "," " " subst split
 
len for
    get dup tonum dup
    nan == if
        drop
        dup len 1 - 2 swap slice
        "-" find dup 2 + rot drop
        rot rot 1 swap slice tonum
        rot rot len rot swap over - 1 + slice tonum
        nip rot drop
        2 tolist for append endfor
    else
        append drop
    endif
endfor
r
pstack