diff.nim

import os, sets, strutils

if paramCount() != 2:
  echo "mydiff file1 file2" 
  quit()

let file1 = open(paramStr(1)) 
let file2 = open(paramStr(2))

let old_lines = file1.readAll().splitLines() 
let new_lines = file2.readAll().splitLines() 

file1.close() 
file2.close()

let old_lines_set = toSet(old_lines) 
let new_lines_set = toSet(new_lines)

let old_added = old_lines_set - new_lines_set 
let old_removed = new_lines_set - old_lines_set

for line in old_lines:
  if line in old_added:
      echo "-", line.strip()
  elif line in old_removed:
      echo "+", line.strip()

for line in new_lines:
  if line in old_added:
      echo "-", line.strip()
  elif line in old_removed:
      echo "+", line.strip()