| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| go/types | Package types declares the data types and implements the algorithms for type-checking of Go packages. |
| golang.org/x/tools/go/callgraph | Package callgraph defines the call graph and various algorithms and utilities to operate on it. |
| golang.org/x/tools/go/ssa | Package ssa defines a representation of the elements of Go programs (packages, types, functions, variables and constants) using a static single-assignment (SSA) form intermediate representation (IR) for the bodies of functions. |
| 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. |