Awesome fu here, thanks. Especially fusing the array traversals and the shift.

It's a bit cryptic though, always the same problem :).

Hi! I wonder if rustc optimizes the two traversals into a single traversal? Does anybody know?

This is one of the best katas I have ever completed! Thanks!

For Rust, when clicking "Attempt", this kata only compiles when the import statement use std::str::FromStr; is added. At first, I did not use FromStr and passed the "Test" step, but could not run "Attempt". Further, the visible tests have the expected solution on the LEFT while the hidden tests have the expected solution on the RIGHT. This confused me during debugging.

You may have commented another version of this solution, but I do not see how primes are recomputed. First, the upper bound is computed, then all primes until the upper bound.

Nice solution, thanks!

   expected: "(* -1 (sin (+ x 1)))"
    but got: "(* -1 (sin (+ 1 x)))"

That should also work. A rule could be that literals should always be on the left hand side (if the operator is commutative).

I agree. I also get:

  expected: "(* -1 (sin (+ x 1)))"
    but got: "-(sin (+ x 1))"

And so on.

I really enjoyed this kata in the beginning, but with all these corner cases, it became a bit of a hazzle. Nice idea though, thank you!

No, it is not needed.

This is smart but extremely slow!