Use nom for parsing

[kinggoesgaming]

nom is useful for efficiently and expressively declare parsing functionality

[onehr]

Thanks, at the very beginning I thought it would be better to use hand-written parser for better error information, but as the progress moves on, I noticed that it would be easier to use parser generator to push the progress, since without actually generating formal IR, it's hard to add optimization or doing semantics checking, so I would consider give it a try to see whether I can push the compiler to a more formal stage. Thanks for your recommendation.