LAMBDA. Is MS Excel now a full fledged programming language?

Microsoft’s researchers believe they’ve now finally transformed Excel into a full-fledged programming language, thanks to the introduction of a new feature called LAMBDA. “With LAMBDA, Excel has become Turing-complete. You can now, in principle, write any computation in the Excel formula language,” a Microsoft blog proclaimed.

“Being Turing complete is the litmus test of a full-fledged programming language,” explained a Visual studio magazine article. And it adds that “early community response has been encouraging,” noting that Microsoft researchers are enthusiastically envisioning skilled Excel users creating functions “that appear seamlessly part of Excel to their colleagues, who simply call them.”

As Microsoft Senior Researcher Jack Williams described it at POPL 2021, “In Excel, it is now possible to build real, full-fledged programming experiences… We can now start to build things that look like real programs.”

Microsoft’s Research blog calls this new LAMBDA feature “a qualitative shift, not just an incremental change.” Named Lambda functions offer programmers the high-quality language-like attributes of “composability” and “re-use,” respecting one of the long-standing principles of good coding, namely not repeating work.

A named function can even become part of another named function elsewhere in the spreadsheet. But that’s just the beginning of what could be even more elaborate constructions, according to the Research blog post. It ultimately envisions “sheet-defined functions” where several different functions, each defined in different cells, are collectively used to define a larger function.