how to use interface in assemblyscript

Question

I'm using thegraph which internally uses https://www.assemblyscript.org/

I'm trying to use interface, but it fails: assert failed.

export interface TransactionData {
  txHash: Bytes;
  timestamp: BigInt;
  logIndex: BigInt;
}

Doesn't assemblyscript support interfaces ? I also tried export type but get the type expected error.

Any idea ?