Unexpected error with escaping characters.

[kohkimakimoto]

• GopherLua is a Lua5.1 implementation. You should be familiar with Lua programming language. Have you read Lua 5.1 reference manual carefully?
• GopherLua is a Lua5.1 implementation. In Lua, to keep it simple, it is more important to remove functionalities rather than to add functionalities unlike other languages . If you are going to introduce some new cool functionalities into the GopherLua code base and the functionalities can be implemented by existing APIs, It should be implemented as a library.

Please answer the following before submitting your issue:

1. What version of GopherLua are you using? :
   commit: 732aa68
2. What version of Go are you using? :
   go version go1.11 darwin/amd64
3. What operating system and processor architecture are you using? :
   Mac OS X 10.14
   Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
4. What did you do? :
   Run print("\z")
5. What did you expect to see? :
   Output z.
6. What did you see instead? :
   Output <string> line:1(column:9) near '\z': Invalid escape sequence.

[kohkimakimoto]

I found that Gopher-lua has a different behavior from lua5.1.
Run the following simple code in the lua and glua REPL.

Lua5.1

Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
> print("\z")
z

Gopher-lua

GopherLua 0.1 Copyright (C) 2015 -2017 Yusuke Inuzuka
> print("\z")
<string> line:1(column:9) near '\z':   Invalid escape sequence

The difference between Lua5.1 and Gopher-lua is the default escaping logic.
Lua5.1 simply save the espaced character if it is non-digit.
see: https://github.com/lua/lua/blob/v5_1_1/llex.c#L302-L303
But Gopher-lua retuns the error.
see:

gopher-lua/parse/lexer.go

Lines 240 to 242 in 732aa68

	buf.WriteByte('\\')
	writeChar(buf, ch)
	return sc.Error(buf.String(), "Invalid escape sequence")