let rec eachindex (size : NTuple) =
    let n = NTuple.getLength size
    if n = 1 then
        let x = NTuple.head size
        <@@ seq { 0..%x-1 } @@>
    else
        let x = NTuple.head size
        let xs = NTuple.tail size
        let expr = eachindex xs

        let tupleType = NTuple.makeType n
        let tupleTypePred = NTuple.makeType (n - 1)

        let init count initializer = callT tupleType <@@ Seq.init @@> [count; initializer]
        let concatMap mapping source = callTR tupleTypePred tupleType <@@ Seq.concatMap @@> [mapping; source]

        expr |> concatMap (lambdaT tupleTypePred
                    (fun smallTupleExpr ->
                        let smallTuple = NTuple.fromExpr smallTupleExpr
                        init x (lambda (fun i ->
                            NTuple.append smallTuple i |> NTuple.toExpr) )))