I said it looks like Kotlin, it's NOT Kotlin. Or this Kata will be much more complicated.

Thank you. Corrected.

In this Kata, function is NOT expression.

According to the tokenize function of JS,

const regex = /\s*(->|[-+*/\(\)\[\]\{\};,]|[A-Za-z]+|[0-9]+)\s*/g;

it will generate something like {_, but it should be { and _.
The correct regex should be

const regex = /\s*(->|[-+*/\(\)\[\]\{\};,]|[A-Za-z_]+|[0-9]+)\s*/g;

the key is [A-Za-z_].

According to the BNF (which is NOT a valid Kotlin BNF)，

function ::= expression "(" [parameters] ")" [lambda]
           | expression lambda

expression ::= nameOrNumber
             | lambda

lambda ::= "{" [lambdaparam "->"] [lambdastmt] "}"

the program {}{}{} is valid. Just pick lambda of expression and expression lambda of function, we can construct a infinite lambda list.

Modify the BNF, or remove this test.

Well then I guess I will just have to add more RegEx tests to validate it :P

Edit: Ok, all fixed on my end. And I cleaned it up a bit. Thanks! :D

OK, I'll tell the author of the js version

Cheers!