Invokes the Objective-C "retain" method.
"retain"
objc
retain pointer => pointer
pointer
A pointer to an Objective-C foreign object.
An argument pointer.
The function retain calls the Objective-C "retain" instance method of pointer to decrement its retain count. The pointer is returned.
retain
release autorelease retain-count
LispWorks Objective-C and Cocoa Interface User Guide and Reference Manual - 21 Mar 2017