Wow, perfect timing! I'm currently writing my first lexer/parser in D as well (http://github.com/landaire/hsc) for a Scheme-like language used in Halo 3. I found Rob Pike's talk on lexical scanning to be pretty useful (https://www.youtube.com/watch?v=HxaD_trXwRE) and I've modeled mine pretty heavily after the text/template lexer: https://golang.org/src/text/template/parse/lex.go.