Stylistic nit only:

```go
var (
	yylval     *yySymType // For storing extra token information, like the contents of a string.
	yyline     int        // Line number within the current file or buffer.
	yypos      int        // Character position within the current line.
	parseMutex sync.Mutex // Mutex protecting the parsing-related global state defined above.
)
```