Source code in the 8th programming language

\ Given a low and high limit, create an array containing the numbers in the
\ range, inclusive:
: n:gen-range \ low hi -- a
  \ make sure they are in order:
  2dup n:> if swap then
  \ fill the array with the values:
  [] ' a:push 
  2swap loop ;

\ Take a string, either "X" or "X-Y", and correctly return either a number (if
\ "X") or an array of numbers (if "X-Y"):
: n:expand-one \ s -- n | a[n,..m]
  \ First see if we can parse a number.  This works in the "X" case:
  dup >n null? if
    \ Failed >n because it's (possibly) "X-Y"
    drop
    \ not a valid number, might be a range
    \ We'll use a capturing regex to handle the different cases correctly:
    /(-?[0-9]+)-(-?[0-9]+)/ tuck r:match 

    \ If the regex matches three (the whole string, plus the two captured
    \ expressions) then it's a valid "X-Y":
    3 n:= if
      1 r:@ >n swap 2 r:@ >n nip
      \ generate the range:
      n:gen-range
    else
      \ The regex didn't match, so we got garbage.  Therefore, return a 'null':
      drop null
    then
  else
    \ It was a "X", just drop the original string:
    nip
  then 
  ;

\ Take an array (possibly) containing other arrays, and flatten any contained
\ arrays so the result is a simple array:
: a:flatten \ a1 -- a2
  [] >r
  (
    nip
    array?  if
      a:flatten r> swap a:+ >r
    else
      r> swap a:push >r
    then
  ) a:each drop r> ;

\ Take a comma-delimited string of ranges, and expand it into an array of
\ numbers:
: n:range-expand \ str -- a
  "," s:/
  ' n:expand-one a:map
  a:flatten ;

\ Process a list:
"-6,-3--1,3-5,7-11,14,15,17-20" 
n:range-expand
\ print the expanded list:
. cr bye