pkg errors, func Unwrap(error) error
pkg go/constant, func Make(interface{}) Value
pkg go/constant, func Val(Value) interface{}
pkg go/token, func IsExported(string) bool
pkg go/token, func IsIdentifier(string) bool
pkg go/token, func IsKeyword(string) bool
pkg go/types, func CheckExpr(*token.FileSet, *Package, token.Pos, ast.Expr, *Info) error
pkg log, func Writer() io.Writer