1. A method for defining a new command in a spreadsheet application, the method comprising: receiving a declaration command in a first spreadsheet cell in the spreadsheet application, the declaration command identifying: a command name for the new command, at least one parameter of the new command, wherein the declaration command includes an identifier of an input cell in the spreadsheet application for the parameter of the new command; and an identifier of an output cell in the spreadsheet application, wherein when the new command is invoked, in a second spreadsheet cell in the spreadsheet application, with a first value supplied as the parameter of the new command, a result of the new command as invoked in the second spreadsheet cell corresponds to a second value in the output cell evaluated with an input identified by the first value being supplied to the input cell in the spreadsheet application.