If the type system will handle it, you can always write your let rec expressions in lambda syntax. If I can do it in LC, you can do it in Ocaml.

See https://en.wikipedia.org/wiki/Let_expression for how to rewrite let rec, and ping me on Discord ( in #lambda-calculus ) for how to do mutual recursion and Y*.

Note that I can't help you with the type system, and I know from Haskell recursive types can be a hassle. I might be able to do the type in Haskell, if that will help you do it in Ocaml ( it really helps here that LC is untyped ).

in c++ error test:
Expected: equal to [unsupported type]
Actual: [unsupported type]

OK - figured out the problem.

Although the show representation was identical, my internal representation of polynomials was ambiguous.
To fix this I needed to implement Eq.

In the field multiplication test I got the result:
Expected x^6 + x^5 + x^4 + x^3 + x^1 + x^0 but got x^6 + x^5 + x^4 + x^3 + x^1 + x^0

I can't see any difference here. What's the problem?

Done, thanks!

For the Java version it would be a nicer experience if the intitial code could at least compile such that all method stubs are filles with return null.

Спасибо, очень доступное объяснение в ролике, все понятно даже не смотря на мой слабый английский

Okay this : Note: Frequency lists with just one or less elements should get rejected. (Because then there is no information we could encode, but the length.).
is missleading, just return the frequency list no matter it's size. Retuning null if freqs.length<=1 cause error in the tests

I keep getting this error :

TypeError: Cannot read property 'map' of null
    at Context.<anonymous> (test.js:122:35)
    at processImmediate (internal/timers.js:464:21)
    ```
But my code ain't 122 line long (only 80) and I don't even use map property in my code.
What am I doing wrong ?

I get that input validations is necessary and all, but I spent more time wondering why would one pass an empty list to encode (I am fine with empty strings) than finding errors in my code. Great kata nevertheless. I would suggest imporoving the functions signatures to remove some redundency in the computations but maybe it is me who wasn't clever enough (though I could ignore some variables but that annoys me even more). Again, great kata.

The let rec construct has some limitations, for example it is not possible to define the list of naturals like so :

let rec nats = 0 :: List.map ((+) 1) nats

The precise explanation of what is or is not acceptable as a right hand side is available in the OCaml manual.

It is meant to be a puzzle. If I provide the algorithm, then what is the challenge? You have to figure out how to reconstruct the shifts by yourselfs. Obviously, you can also google it.

Good kata but I found decoding instrution not intuitive, in my opinion it should be extended.
Current simple explanation is not sufficient and if someone doesn't know the IBWT then it will be hard to proceed based only on description from excercise.

This solution was meant to expose the lazy testing of this kata. My actual solution is here: https://www.codewars.com/kata/reviews/54e4b5cfd5e01959820000b5/groups/55e36e2cda32c7934600006e