Fast Sheet-Defined Functions in Spreadsheets

May 21, 2009
2:50 pm - 4:00 pm
Halligan 111
Speaker: Peter Sestoft


Abstract: Spreadsheets appeal to millions of users because they are concrete, declarative and non-iterative. However, the absence of abstraction facilities leads to models that are unwieldy, slow, error-ridden and difficult to maintain.

Hence users should be able to define new functions within the familiar spreadsheet paradigm, without resorting to external languages such as VBA in Excel, and with speed comparable to built- in functions.

We present a prototype spreadsheet implementation that achieves these goals, based on the concept of sheet-defined function. Type analysis and continuation-based compilation are used to generate efficient .NET bytecode from such sheet-defined functions at runtime. Thanks to the platform's just-in-time compiler the implementation is fast.

We give several examples of useful functions definable this way. We show that higher-order and recursive sheet-defined functions have natural uses. For instance, the Goal Seek numerical equation solver, and several other built-in functions from Excel, can be user-defined in our framework.

In future work, we expect to support functions with a carefully limited form of state, and possibly to exploit the near-explicit parallelism of spreadsheet models.