4.19 Undefined
The constant #<undefined> is used as the initial value for letrec bindings and in other places where a placeholder value is needed before a specific value can be assigned. Use undefined (which is bound to #<undefined>) as a last resort.
The #<undefined> value is always eq? to itself.
| (require racket/undefined) | package: base |
The bindings documented in this section are provided by the racket/undefined library, not racket/base or racket.
The #<undefined> constant.
Added in version 6.0.0.6 of package base.