I would like to mention that most, if not all, of the Go compiler and related utilities is written in Go itself, with high quality, open source code that can be found in the "go" package of the standard library:
I would recommend using that as a template for one's own compiler, because it's written in idiomatic Go (originally by the language creators) and is cleanly split across abstraction boundaries (packages "scanner", "parser", "ast", and so on.)
There's also a smaller, simpler parser in the "text/template/parse" package, that is used to parse the templating languages in "text/template" and "html/template". As an introduction to it, I recommend the talk "Lexical Scanning in Go" by Rob Pike: