Naively this is quite surprising, but the devil is in the details. With the exception of Lean I'd point out they're all fairly close: Chez being 2.5x slower than C++ is not ignorable but it's also quite good for a dynamically-typed JITted language[1]. And I'm not surprised that F# does so well at this particular task. Without looking into it more closely, this seems to be a story about F# on .NET Core having the most mature and painless out-of-the-box parallelism of these languages. I assume this is elapsed time, it would be interesting to see a breakdown of CPU time.

I don't think these results are quite comparable because of slightly differing parallelism strategies; I'd expect the F# implementation of just spinning off threads to be more a little more performant than a Rayon parallel iterator, which presumably has some overhead. But that really just shows how hard it is to do a cross-language comparison; Rust and C++ can certainly be made faster than the F# code by carefully manipulating a ton of low-level OS concurrency primitives. This would arguably also be little misleading. Likewise Chez and Haskell have good C FFI; does that count? It's a tricky and highly qualitative analysis.

[1] FYI, one possible performance improvement with the Chez code is keeping the permutations in fxvectors and replace math operations with the fixnum-specific equivalent - this tells the compiler/interpreter that the data are guaranteed to be machine integers rather than bigints, so they aren't boxed/unboxed. I am not sure without running it myself, but there seems to be avoidable allocations in the Chez implementation. https://cisco.github.io/ChezScheme/csug/objects.html#./objec...