A simple implemtation of Reverse Polish Notation using Lark. My mom always used to mention she preferred Reverse Polish notation back in college. Since I never really studied the format, it still looks alien to me. Given the simplicity of the "language", it was a good choice to practice lark transformers and get a little better at parsing it myself :).
Reverse Polish Notation uses prefix notation. Therefore the expression 1 + 2 is instead represented as + 1 2. In a larger example, 1 + 2 + 3 = + 1 + 2 3.
To reduce an expression in Reverse Polish Notation, find the first cluster of (OPERATOR NUMBER NUMBER) and reduce it to a single value. Repeat this process until a single value remains.
* * + 3 2 - 5 1 - 6 2 = * * 5 - 5 1 - 6 2 ( + 3 2 = 5)
= * * 5 4 - 6 2 ( - 5 1 = 4)
= * * 5 4 4 ( - 6 2 = 4)
= * 20 4 ( * 5 4 = 20)
= 80 ( * 20 4 = 80)
Note: like standard notation, you should expect there to always be 1 fewer operators than values. If this is not the case, either the initial expression is invalid or you've messed up somewhere.
Run pytest .\tests.py.