[[Hewlett-Packard|HP]]'s [[RPL (programming language)|RPL]], first introduced in the [[HP-18C]] calculator in 1986, is a type of proprietary hybrid direct-threaded and indirect-threaded threaded-interpreted language that, unlike others TILs, allows embedding of RPL "objects" into the "runstream" iei.e. Thethe stream of addresses through which the interpreter pointer advances. An RPL "object" can be thought of as a special data type whose in-memory structure contains an address to an "object prolog" at the start of the object, and then data or executable code follows. The object prolog determines how the object's body should be executed or processed. Using the "RPL inner loop",<ref name="RPL1">Busby, Jonathan. [https://www.hpmuseum.org/forum/thread-11358.html "The RPL inner loop explained"], [http://www.hpmuseum.org/ "The Museum of HP Calculators"], 7 September 2018, Retrieved on 27 December 2019</ref> which was invented and published (and patented <ref>{{cite web |author-last=Wickes |author-first=William C. |title=Data processing system and method for the direct and indirect execution of uniformly structured object types |website=uspto.gov |date=30 May 30, 1986 |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=8&p=1&f=G&l=50&d=PTXT&S1=((%22Hewlett+Packard%22.ASNM.)+AND+Wickes.INNM.)&OS=AN/%22Hewlett+Packard%22+and+IN/Wickes&RS=(AN/%22Hewlett+Packard%22+AND+IN/Wickes) |access-date = 27 December 27, 2019}}</ref>) by William C. Wickes in 1986 and published in "Programming Environments", Institute for Applied Forth Research, Inc., 1988, execution follows like so:
# Dereference the IP (instruction pointer) and store it into O (current object pointer)
