Create fields with a parametric type


I have a parametric type Slot and I would like its parent / children to be also parametric type Slot.
I tried something like this

extendable entity type Slot<A: Asset, C: AssetSlotConnection> schema name ‘STRUCT_SLOT’ {

parent: mixing Slot

children: [mixing Slot] (parent)

and I’m getting the following provisioning error:

[foundation/prod] Created 939.01Kb ZIP of 7 packages in 0.7s
[foundation/prod] Server Errors: (2018-02-07T13:39:09.071-08:00)
{fileUrl:“unknown”,lineNum:-1,colNum:-1,severity:“ERROR”,message:“type doesn’t have exactly one variable”,code:“NOT_CLASSIFIED”}