function spout(integer first, integer this, sequence s)
string res
    if first=this-1 then
        res = sprintf("%d",s[first])
    else
        res = sprintf("%d%s%d",{s[first],iff(first=this-2?',':'-'),s[this-1]})
    end if
    return res
end function

function extract_ranges(sequence s)
integer first = 1
string out = ""
    if length(s)!=0 then
        for i=2 to length(s) do
            if s[i]!=s[i-1]+1 then
                out &= spout(first,i,s)&','
                first = i
            end if
        end for
        out &= spout(first,length(s)+1,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}))