Source code in the icon programming language

procedure count (test_item, str)
  result := 0
  every item := !str do 
    if test_item == item then result +:= 1
  return result
end

procedure is_self_describing (n)
  ns := string (n) # convert to a string
  every i := 1 to *ns do {
    if count (string(i-1), ns) ~= ns[i] then fail
  }
  return 1 # success
end

# generator for creating self_describing_numbers
procedure self_describing_numbers ()
  n := 1
  repeat {
    if is_self_describing(n) then suspend n
    n +:= 1
  }
end

procedure main ()
  # write the first 4 self-describing numbers
  every write (self_describing_numbers ()\4)
end


procedure is_self_describing (n)
  ns := string (n) # convert to a string
  every i := 1 to *ns do {
      if count (string(i-1), ns) ~= ns[i] then fail
      }
  return n # on success, return the self-described number
end
 
procedure self_describing_numbers ()
  suspend is_self_describing(seq())
end