| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| go/ast | Package ast declares the types used to represent syntax trees for Go packages. |
| 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. |
| golang.org/x/tools/go/ast/astutil | Package astutil contains common utilities for working with the Go AST. |
| golang.org/x/tools/go/types/typeutil | Package typeutil defines various utilities for types, such as Map, a mapping from types.Type to interface{} values. |