Vim9 lambda function destructuring a list in arguments?

Question

I tried to destructure a list in a lambda function, like this:

var matched = reduce(
    mapnew(lines, (_, x) => [strpart(x, 0, 1), strpart(x, 2, 1)]), 
    (acc, [a, b]) => acc && a == "a" && b == "b",
    1)

It seems [a, b] in the lambda arguments is not possible. Is there another way to name items of this list without resorting to indexing the array directly?

Answer 1

Move de-structuring out explicitly. (untested code)

var reducer = (acc, parts) => {
    [a, b] = parts
    return acc && a == "a" && b == "b"
    }
var matched = lines
    ->mapnew((_, x) => [strpart(x, 0, 1), strpart(x, 2, 1)])
    ->reduce( reducer, 1)