The Future of Programming Languages: Tim Sweeney’s Vision for a Functional Logic Revolution

In a wide-ranging conversation with Lex Fridman, Epic Games founder and CEO Tim Sweeney outlined his ambitious vision for the future of programming languages, particularly focusing on the development of “verse,” a functional logic language designed to power the metaverse.

Sweeney, whose company created the Unreal Engine and hit games like Fortnite, is advocating for a fundamental shift in how programming languages work. “The programming language should achieve a high degree of power not by having a lot of features but by having a small number of features that work together,” Sweeney explained, citing Niklaus Wirth, creator of Pascal.

The core innovation in functional logic languages like verse is how they handle expressions. While traditional languages produce a single value from an expression, functional logic languages can produce zero, one, or multiple values. This seemingly subtle difference creates powerful new possibilities for programming constructs like conditional statements and loops.

“In a functional logic language, your condition would either succeed and produce a value or it would fail,” Sweeney explained. “The exciting thing is your expression can produce values and bind variables that are then accessed by the ‘then’ branch.”

This approach allows for more sophisticated programming patterns that resemble database queries, bringing “the power of SQL queries” into a general-purpose programming language. According to Sweeney, this creates a more intuitive model for beginners. Remarkably, new programmers learning verse through Fortnite are grasping these concepts naturally: “They just assume programming works this way and they’re writing way more advanced and interesting for loops and conditions than we’re often writing internally.”

Beyond expressiveness, Sweeney emphasized the critical importance of correctness and type safety for the metaverse. With a constantly evolving codebase created by countless authors, the ability to verify compatibility and correctness becomes paramount. “The cost of fixing a bug that’s made it through to runtime and is in users’ hands is hundreds of times higher than fixing a bug that you’ve just observed as you’re running your code yourself,” he noted.

Sweeney referenced the Curry-Howard correspondence, a foundational mathematical result from the 1930s establishing the relationship between computer programs and mathematical proofs. This connection allows programming languages with properly designed type systems to express and verify mathematical theorems. “If you design a type system in a certain way, then your types can express theorems,” Sweeney explained, adding that verse aims to be “the first mainstream programming language that fully adopts that approach.”

Perhaps most ambitious is verse’s approach to concurrency. The language uses transactional memory to enable massive parallelism without requiring programmers to manually manage thread synchronization. “We’re going to have programmers write completely ordinary code that reads and writes variables in the completely ordinary way, and they’re not going to have to worry about concurrency at all,” Sweeney said.

This system runs updates “speculatively,” tracking changes locally rather than immediately modifying global state. After execution, the system determines which operations had no conflicts and can be safely committed. This approach could eventually enable simulations with “tens of millions of people together in one scene,” vastly exceeding the current 100-player limit in Fortnite.

By shifting the complexity of concurrency from individual programmers to the language itself, Sweeney hopes to make massive-scale programming accessible even to hobbyists and first-time coders. “We’re moving this from being a programming problem for the programmer to deal with to being a language problem for us language designers to deal with,” he concluded.