My knowledge of reverse polish notation came in handy today. It’s weird how these things come up in real life and not just in an academic setting. Granted, not every college graduate deals with the Excel file format.

Excel’s formulas are stored in binary spreadsheet files in reverse polish notation, which makes sense. There aren’t usually numbers in the file which say how many arguments a function contains, so we have to know that in advance to be able to understand the formula. You evaluate the arguments of a formula before the formula itself, so the stack at the point of evaluating the formula itself should contain exactly the number of arguments the formula has. It’s elegant when it works, but it makes it difficult to figure out when you have an error (unlike in XML where everything has boundaries)

Usually, if you read in more arguments than are available, an exception is thrown, and if you read in too few, an exception is thrown when evaluation completes and you have extra tokens to read. You could theoretically read too few arguments at one point and too many at another and just have an invalid result, but that would require two errors happening simultaneously, which is (hopefully) improbable.