Seq

gistfile1.coffee

seq = (a, b = a) ->
  if typeof a == "number" and (a == b or typeof b == "number")
    if a != b
      "(#{a}..#{b})"
    else
      "(0..#{a})"
  else if typeof a != "string" or !rgx.test a or a == ""
    "(0..1)"
  else
    [ok, start, end] = a.match rgx
    end = (+end) + 1
    "(#{start}..#{end})"

com = (s) ->
  if rgx.test s
    [ok, start, end] = s.match rgx
    start = +start
    end = +end
    (end - start + 1) * (start + end) / 2

gistfile2.js

>>> seq()

"(0..1)"

>>>  seq(seq())

"(0..2)"

>>>  seq(seq(seq(2, 3)))

"(2..5)"

>>>  com(seq(15)); 

120

>>>  com(seq(seq(15))); 

136

>>>  com(seq(seq(15, 33))); 

490