Write the expression one way round and it’s Polish notation, the other way and it’s Reverse Polish notation. Then the second lesson is that the “Reverse” part is important, but a smokescreen that relates only to the direction in which it is written.
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Perhaps we Anglophones should put in a bit of effort to learn how to pronounce his name. The first thing to learn about RPN is that the “Polish” part comes from Łukasiewicz’s nationality. Simply put, RPN is a specific method of writing math equations that is still human while being suitable for input into a computer with limited memory.
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I had not previously encountered him so this opened up a fascinating exploration of his work, plus a revisiting of RPN as an adult rather than as a soldering-iron-wielding teen. I was reminded of my Sinclair Scientific recently when I read a Hackaday comment which introduced the inventor of RPN, Jan Łukasiewicz, as an engineer rather than a mathematician. It spent several years on my bench before being reverently placed in a storage box of Sinclair curios which I’ve spent half a day turning the house over to find as I write this article. The handy sticker inside the case explained the mystery, this machine used so-called Reverse Polish Notation, or RPN. This one looked more akin to a run-of-the-mill arithmetic calculator, but had button modes for trigonometric functions and oddly an enter key rather than an equals sign. It had a set of corroded batteries that had damaged one of its terminals, but with the application of a bit of copper strip I had a working calculator.Īnd what a calculator! It didn’t have many buttons at a time when you judged how cool a scientific calculator was by the prolific nature of its keyboard.
Protected by a smart plastic case, it was a pretty good condition Sinclair Scientific that turned out when I got it home to have 1975 date codes on its chips, and since anything with a Sinclair badge was worth having it became mine for a trifling amount of money. Sometime in the 1980s when I was a spotty teen, I picked up a calculator at a rummage sale.
But I assure you it’s not only real, but a true gem in the evolution of computing. I know what you’re thinking… RPN sounds like a sales gimmick and I got taken for a fool. The best rummage sale purchase I ever made was a piece of hardware that used Reverse Polish Notation.
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