Convert Sum Types to Integers

[keyan-m]

What is your idea? Provide a use case.

Inspired by the optimization done by @MicroProofs in Bullet, it seems like a low-hanging fruit to auto-convert to integers any sum types that none of their constructors hold values.

As an example, if a datum carries a boolean, its False (or True, not sure which has index 0 😅) is encoded as d87980 in CBOR. This can be reduced by 2 bytes to a simple 00 in CBOR to represent the index without the overhead.

Why is it a good idea?

Currently data encoding of sum types translate to the Constr variant of Data, which carries an index, and a list of data values:

data Data
  = Constr Integer [Data]
  | Map [(Data, Data)]
  | List [Data]
  | Int Integer
  | B ByteString

This list is always empty for constructors without values (e.g. True and False of Bool). So this empty list becomes an unused overhead.

By having the compiler auto-convert such sum types, we get to drop the empty list and reduce on-chain data bloat.

What is the current alternative and why is it not good enough?

Using builtin.unconstr_index gives a cheap access to the index of a Constr (as implemented here in Bullet). However, this can reduce maintainability of the code as the compiler won't be able to catch changes to the underlying sum type.

[keyan-m]

Thinking more about this, making it into something customizable might be better (e.g. a contract that needs to incorporate a datum from another contract not written in Aiken).

Perhaps it makes sense to include this in #1100?

[emiflake]

I would agree that a decorator would make the most sense for this feature and I definitely would like to see this too. A lot of on-chain code that isn't written using Aiken uses this encoding for enums.