let arr = [1;2;3;4]

// sum all elements
let sum seq =
    seq |> Seq.fold (fun acc e -> acc + e) 0

let sum2 seq =
    seq |> Seq.fold (+) 0


let sumFun a b =
    a + b

let sum3 seq = seq |> Seq.fold sumFun 0

let sum4 seq = Seq.fold sumFun 0 seq


(sum arr).Dump()
(sum2 arr).Dump()
(sum3 arr).Dump()
(sum4 arr).Dump()