Via Gruber, a post by Instapaper's Marco about interface metaphors, and a brief iPad-related response from Chris Clark. Marco uses the Calculator app as an example of when not to emulate a physical interface in a computer application, and mentions Soulver, an awesome-looking calculator app for Mac OS X.

For quick calculations, my calculator of choice is Spotlight. Yes, Spotlight, the little magnifying glass in the upper-right corner of the Mac OS X screen that lets you do text search queries of your computer. If you type an arithmetic expression, the answer is the first "result" in the Spotlight menu. And since Spotlight is always available via keyboard (Command-Space by default), it's the fastest way I know to do simple arithmetic. (I also use Spotlight as a dictionary, and begrudgingly use it as an application launcher. It's pretty much useless for anything else. And yes, I know of the alternatives.)

It's interesting that Marco would bring the calculator example to the table in a discussion about iPad interfaces, because a calculator app for the iPad/iPhone is a prime candidate for emulating the desktop calculator interface. It's a touch interface, so we still need buttons to press to enter data into the calculator. Were Acqualia to port Soulver to the iPad, I'd expect to find a custom calculator-like keypad at the bottom of the screen, at the very least. [Update 3/13: Of course there's an iPhone version of Soulver, with a keypad.]

I want an Emacs port of Soulver. Maybe I'll write one. Of course, Emacs has a fancy calculator built in, and it includes a Reverse Polish Notation mode. (EmacsWiki on Calc.) But I like the idea of a textual calculator with real-time spreadsheet-like capabilities. And there are spreadsheet apps for Emacs, too: Simple Emacs Spreadsheet, Dismal, esheet.