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Urple.java | 12.13 KB |

The HP-48 programming language, RPL, and its variants User RPL and System RPL are very dear to me. I spent hundreds, thousands, possibly billions of hours programming my two HP-48GX calculators back in high school.

RPL is unlike any programming language you have ever programmed in. There is somewhat of an introduction at the HP Museum, so I won't attempt to detail it. Basically, you have a stack, and your program looks like:

`« 1 X SQ SWAP - SQRT »`

...which would calculate √(x²-1). Here, 1 gets pushed onto the stack, then the value of x (you could single-quote x if you wanted to delay evaluation). Then `SQ`

squares the value on the top of the stack. Next, `SWAP`

swaps the top two values on the stack, so that the next step subtracts 1 from x² instead of the other way 'round. Then `SQRT`

takes the square root of that.

Urple is a very poor, minimal Java implementation of some of the basic methods of User RPL. It doesn't even have conditionals and loops yet. It's basically just a calculator like the venerable Unix `dc`

. If you want a real RPN calculator, check out Orpie—fantastic stuff!