f# sequence of running total

Use List.scan:

let runningTotal = List.scan (+) 0 >> List.tail

[1; 2; 3; 4]
|> runningTotal
|> printfn "%A"

Seq.scan-based implementation:

let runningTotal seq' = (Seq.head seq', Seq.skip 1 seq') ||> Seq.scan (+)

{ 1..4 }
|> runningTotal
|> printfn "%A"

Another variation using Seq.scan (Seq.skip 1 gets rid of the leading zero):

> {1..4} |> Seq.scan (+) 0 |> Seq.skip 1;;
val it : seq<int> = seq [1; 3; 6; 10]

> Seq.scan (fun acc n -> acc + n) 0 [1;2;3;4];;
val it : seq<int> = seq [0; 1; 3; 6; ...]

With lists:

> [1;2;3;4] |> List.scan (fun acc n -> acc + n) 0 |> List.tail;;
val it : int list = [1; 3; 6; 10]

Edit: Another way with sequences:

let sum s = seq {
    let x = ref 0
    for i in s do
        x := !x + i
        yield !x
}

Yes, there's a mutable variable, but I find it more readable (if you want to get rid of the leading 0).

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