The Ultimate Technical Flex: Coding a Turing Machine in Excel
Description
This image continues the 'bizarre coding interview' meme format with a screenshot of a tweet from user Joey (@joeyjjooste). The tweet reads: 'The most bizarre coding interview I've ever done was at Facebook when as usual I asked a candidate to write in any language of their choice.. And they nonchalantly said "I'll write it in Microsoft Excel 2012", to which I almost let loose a chuckle until...'. Below this text is a screenshot of a Microsoft Excel window. The file is named 'Turing Machine_Successor.xlsx' and the spreadsheet is filled with intricate formulas, including a visible one using IFERROR, VLOOKUP, and INDEX functions. The sheet tabs are labeled 'Machine', 'State Table', and 'Directions', indicating a complex computational model. The humor is aimed at a highly technical audience who understands that while Excel is not a conventional programming language, its formula engine is Turing-complete. Building a Turing Machine, a foundational concept of theoretical computer science, within Excel is a monumentally complex and impractical feat, making it an ultimate 'technical flex' that showcases deep knowledge of both CS theory and the unexpected capabilities of a common business tool
Comments
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The candidate got the job, but their first performance review was just a series of #REF! errors and a circular dependency warning from HR
The minute he encoded the Turing machine with nested VLOOKUPs, my only architectural concern became: how do we get meaningful code reviews when Git diff thinks the entire .xlsx changed?
That candidate just proved Excel is Turing complete while simultaneously demonstrating why we need dependency injection frameworks for VLOOKUP chains
When the candidate said they'd implement a Turing machine in Excel, the interviewer thought they were joking - until they realized Excel formulas are Turing complete and this madlad actually built a state machine with nested VLOOKUPs. Suddenly 'any language of their choice' became a careful lesson in specification: next time, explicitly exclude spreadsheet software, or you'll spend the entire interview watching someone debug circular reference errors in what should have been a simple linked list traversal. At least they didn't choose PowerPoint animations
Offer any language and someone ships a VLOOKUP/IFERROR Turing machine - zero dependencies, instant CFO adoption, and better LTS than half your microservices
Excel as a Turing machine: infinite tape via infinite rows, state machine via nested IFs - proving Church-Turing with A1 notation, no lambda needed
Ask for any language and you’ll get Excel - Turing‑complete, PM‑compatible, and the only runtime where VLOOKUP doubles as dependency injection