お題: http://ideone.com/IcHcrV

sum.fsx

type subject = {point: int}
type student = {subjects: subject list}
type classroom = {students: student list}


let data = {students = [
        {subjects = [{point = 10}; {point = 20}]}
        {subjects = [{point = 20}; {point = 30}]}
        {subjects = [{point = 30}; {point = 40}]}
        {subjects = [{point = 40}; {point = 50}]}
    ]}
// クラス合計
let classSum =
    data.students
    |> List.collect (fun x -> x.subjects)
    |> List.sumBy (fun x -> x.point)

// 生徒ごとの合計
let studentsSum =
    data.students
    |> List.map (fun x ->
        x.subjects
        |> List.sumBy (fun x -> x.point))
        
// おまけでseq式
let classSum2 =
    seq {
        for x in data.students do
        for x in x.subjects do
        yield x.point
    }
    |> Seq.sum
let studentsSum2 =
    seq {
        for x in data.students do
        yield seq {
            for x in x.subjects do
            yield x.point
        } |> Seq.sum
    } |> Seq.toList