Spreadsheet 2.0 / Product Requirements Document

We've done some focus group studies and some market research, and found that customers are really excited about Spreadsheet 1.0. In fact, we've gotten so many requests that we're going to release the next version as our flagship product. Marketing is really excited about the potential of Spreadsheet 2.0.

But they want a few changes...

Feature: User-friendly cell references.

Marketing wants to use references like "A1", "B2", etc. instead of row/column indexes like (1,1).
Internally, we can still use numbers, but the whole UI has to use the letter/number combinations, for both input and output. So instead of
set 1 1 57
we now do
set B1 45.3

Feature: Function display.

We want to be able to display (print) the function associated with a cell as well as the value. For example, if the cell is calculating A1+B2, we should have a way to print "A1+B2" on the display.
We should also have a way to display the entire spreadsheet this way, showing the formulas instead of the values. (Of course, any cells without formulas still show their values.)

Feature: Trig functions.

There's a big customer who really wants sin and cos functions. So we have to have these in version 2.

Feature: User defined formulas.

Market research indicates that users want to set up their own functions. So in version 2, we'll let users set functions on cells. And not just simple functions; we'll let them set up any function that can be built up from +,/,*,-,%, sin, cos, (, and ), as well as any other functions or operators we come up with in the future. The syntax will look like
set B1 = C2+ D3 * (1.5 + B7 + sin(A4) )
The = means that we're setting a function, not a value. Note that the formula can contain cell references and constant numbers, and that there isn't necessarily white space between the terminal elements.

Feature: Embeddability

Another big customer really wants to embed this spreadsheet into their hand-held computing device. They have their own methods for I/O (involving handwriting recognition), and so they just want a nice C++ interface to our spreadsheet library with no I/O built in. In other words, they want to be able to create a Spreadsheet, set and get cell values and formulas, etc, but they don't want an event loop. We should be able to build our code into a library to hand off to them.


A reasonable way to implement the user defined formulas is to implement a recursive descent parser. (Other ways are to build an abstract syntax tree or use a parser generator like yacc.) Note that the parser will have to be able to do two different things: (1) find all the cell references in the formula in order to figure out what cells the formula depends on; (2) actually calculate the value of the formula. These things happen at different times.

Possible Future Extensions