function starts_with(s, sub)
  return s:find(sub, 1, --[[no escapes]] true) == 1

function starts_with(s, prefix)
  if #s < #prefix then
    return false
  end
  for i=1,#prefix do
    if s:sub(i,i) ~= prefix:sub(i,i) then
      return false
    end
  end
  return true

function ends_with(s, sub)
  return s:reverse():find(sub:reverse(), 1, --[[no escapes]] true) == 1

function ends_with(s, suffix)
  if #s < #suffix then
    return false
  end
  for i=0,#suffix-1 do
    if s:sub(#s-i,#s-i) ~= suffix:sub(#suffix-i,#suffix-i) then
      return false
    end
  end
  return true

    left = left,
    right = right,

    left = math.floor(left),
    right = math.floor(right),

    -- give some time for the OS to flush everything to disk
    love.timer.sleep(0.1)

--?   print('press')

--?   print('press', State.selection1.line, State.selection1.pos)

  assert(#State.lines == #State.line_cache)

  if #State.lines ~= #State.line_cache then
    print(('line_cache is out of date; %d when it should be %d'):format(#State.line_cache, #State.lines))
    assert(false)
  end