http://www.antlr.org/about.html
https://github.com/antlr/antlr4/blob/4.6/doc/index.md
http://www4.di.uminho.pt/~gepl/GQE/documents/books/Pragmatic.The.Definitive.ANTLR.4.Reference.Jan.2013.pdf
https://github.com/Nelson0409/Little-Language-Compiler/blob/master/The%20Definitive%20ANTLR%204%20Reference.pdf