ABI: Placeholder - Support calling an ARC-4 Application

[michaeldiamant]

Problem

Placeholder: Expect the ticket to be broken out into multiple tickets when we pick up the effort.

https://github.com/algorandfoundation/ARCs/blob/main/ARCs/arc-0004.md defines a protocol for calling ARC-4 Applications. To close the PyTeal ABI support gap, the ticket requests 1st class support for defining PyTeal applications calling an ARC-4 Application.

Solution

Dependencies

Urgency

[jasonpaulos]

Completed by #387