SqlReader.fs

type Transaction<'a> = string -> 'a
module Transaction = 
    let map<'a,'b> (mapper:'a -> 'b) (t:Transaction<'a>) : Transaction<'b> = 
        (fun x -> mapper (t x))
    let bind<'a,'b> (binder:'a -> Transaction<'b>) (t:Transaction<'a>) : Transaction<'b> = 
        (fun x -> binder (t x) x)
    let execute connectionString (t:Transaction<'a>) = 
        t ConnectionString

type SqlReader<'state, 'element> = 
    abstract member Read : reader:('state -> System.Data.IDataReader -> 'element -> 'state*bool) -> 'state -> Transaction<'state>

module SqlReader = 
    let read<'state,'element> reader state (x:SqlReader<'state, 'element>) = x.Read reader state
    let fold<'state, 'element> folder = read<'state, 'element> (fun s _r x -> (folder s x), true)
    let readList<'a> = fold<_ list, 'a> (fun s x -> x::s) [] >> Transaction.map List.rev
    let optional<'a> = read<_ option, 'a> (fun s _r x -> (Some x), false) None
    let single<'a> = optional<'a> >> Transaction.map (Option.defaultWith (fun () -> failwithf "Expected one row, got zero"))
    let genericList<'a> = new System.Collections.Generic.List<'a>() |> fold<_, 'a> (fun s x -> s.Add(x); s) 
    
let a : int = 
    SqlReaderProvider<"SELECT @n AS N">.Query(5)
    |> SqlReader.single
    |> Transaction.execute
()