Fibonacci in Roc by ChatGPT

fib.roc

module [Fibonacci]

## Returns the Fibonacci sequence up to the nth term.
fibonacci : U32 -> List U32
fibonacci = \n ->
    if n == 0 then
        []
    else if n == 1 then
        [0]
    else
        List.range 0 (n - 1)
        |> List.foldl (\idx, acc ->
            if idx == 0 then
                List.concat acc [0]
            else if idx == 1 then
                List.concat acc [1]
            else
                let
                    last = List.get (List.len acc - 1) acc
                    secondLast = List.get (List.len acc - 2) acc
                in
                    List.concat acc [(last + secondLast)]
        ) []

## Test cases
expect fibonacci 0 == []
expect fibonacci 1 == [0]
expect fibonacci 2 == [0, 1]
expect fibonacci 5 == [0, 1, 1, 2, 3]
expect fibonacci 10 == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]