| bytes | Package bytes implements functions for the manipulation of byte slices. |
| go/ast | Package ast declares the types used to represent syntax trees for Go packages. |
| go/printer | Package printer implements printing of AST nodes. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| go/types | Package types declares the data types and implements the algorithms for type-checking of Go packages. |
| io/ioutil | Package ioutil implements some I/O utility functions. |