Parsing Lua strings, more specifically newlines - parsing

Question

I'm trying to parse Lua 5.3 strings. However, I encountered an issue. For example,
$ lua
Lua 5.3.4 Copyright (C) 1994-2017 Lua.org, PUC-Rio
> print(load('return "\\z \n\r \n\r \r\n \n \n \\x"', "#test"))
nil test:6: hexadecimal digit expected near '"\x"'
>
> print(load('return "\\z\n\r\n\r\r\n\n\n\\x"', "#test"))
nil test:6: hexadecimal digit expected near '"\x"'
Both of these error on line 6, and the logic behind that is pretty simple: eat newline characters (\r or \n) if they're different from the current one (I believe this to be an accurate description of how the lua lexer works, but I may be wrong).
I have this code, which should do it:
local ln = 1
local skip = false
local mode = 0
local prev
for at, crlf in eaten:gmatch('()[\r\n]') do
local last = eaten:sub(at-1, at-1)
if skip and prev == last and last ~= crlf then
skip = false
else
skip = true
ln = ln + 1
end
prev = crlf
end
It decides whether to eat newlines based on the previous char. Now, from what I can tell, this should work, but no matter what I do it doesn't seem to work. Other attempts have made it report 5 lines, while this one makes it report 9(!). What am I missing here? I'm running this on Lua 5.2.4.
This is part of a routine for parsing \z:
local function parse52(s)
local startChar = string.sub(s,1,1)
if startChar~="'" and startChar~='"' then
error("not a string", 0)
end
local c = 0
local ln = 1
local t = {}
local nj = 1
local eos = #s
local pat = "^(.-)([\\" .. startChar .. "\r\n])"
local mkerr = function(emsg, ...)
error(string.format('[%s]:%d: ' .. emsg, s, ln, ...), 0)
end
local lnj
repeat
lnj = nj
local i, j, part, k = string.find(s, pat, nj + 1, false)
if i then
c = c + 1
t[c] = part
if simpleEscapes[v] then
--[[ some code, some elseifs, some more code ]]
elseif v == "z" then
local eaten, np = s:match("^([\t\n\v\f\r ]*)%f[^\t\n\v\f\r ]()", nj+1)
local p=np
nj = p-1
--[[ the newline counting routine above ]]
--[[ some other elseifs ]]
end
else
nj = nil
end
until not nj
if s:sub(-1, -1) ~= startChar then
mkerr("unfinished string near <eof>")
end
return table.concat(t)
end

Answer 1

Compact code for iterating lines of Lua script:
local text = "First\n\r\n\r\r\n\n\nSixth"
local ln = 1
for line, newline in text:gmatch"([^\r\n]*)([\r\n]*)" do
print(ln, line)
ln = ln + #newline:gsub("\n+", "\0%0\0"):gsub(".%z.", "."):gsub("%z", "")
end
Efficient code for iterating lines of Lua script:
local text = "First\n\r\n\r\r\n\n\nSixth"
local sub = string.sub
local ln = 1
for line, newline in text:gmatch'([^\r\n]*)([\r\n]*)' do
print(ln, line)
local pos, max_pos = 1, #newline
while pos <= max_pos do
local crlf = sub(newline, pos, pos + 1)
if crlf == "\r\n" or crlf == "\n\r" then
pos = pos + 2
else
pos = pos + 1
end
ln = ln + 1
end
end