8.12
4.5 Optional Values
An optional value encapsulates a result that either is present or absent. This data type is particularly useful for the return value of element lookups in collections, or for procedures that have a trivial notion of failure.
constructor
(present value)
Container for a value.
constructor
Represents a lack of a value.
procedure
(option-case opt #:present present-proc #:absent absent-proc) → any/c opt : option? present-proc : (λ/c any/c → any/c) absent-proc : (λ/c → any/c)