Not nonexistent-- there are many stack-oriented programming languages[1], of which Forth is the most famous.

There's even a "Reverse Polish Lisp" on HP calculators!

[1] http://en.wikipedia.org/wiki/List_of_programming_languages_b...

See also http://en.wikipedia.org/wiki/Reverse_Polish_notation#Current...

Sorry, I meant there is no benefit to using it in programming languages.

Forth is arguably the best language in terms of expressive power/language complexity, though that's largely due to the denominator.

It's a great choice for tightly constrained devices, though far fewer devices have such constraints now. The mental overhead of having to track stack-effects for each function makes it difficult to scale to large systems and maintain productivity, but if you're trying to eke every iota of power out of a chip with a tiny amount of ROM, it's hard to beat a direct-threaded (or token-threaded...) Forth.

> Lisp and related languages use Polish Notation everywhere.

> The main benefit is that (R)PN is parenthesis-free

... so what you're saying is Lisp has all those parenthesis just to troll us?

Seriously though, using PN can make implementing parsers a lot simpler as it makes the grammar less ambiguous.

I don't know about less ambiguous, it can still require only single token lookahead and be context-free without any parentheses, but Lisp-ish languages are easier to parse because you have fewer productions to worry about compared to more complex languages.