evaluateTransaction should work with utxos that only exist in the mempool.

[AndrewWestberg]

What is your idea? Provide a use case.

Chaining transactions is currently a good way to get a lot of transactions on chain in Cardano. This involves utilizing utxos that only exist in the mempool as a result of previous transaction. These transactions are not yet on chain, but it can be much faster to make follow-up transactions. submitTransaction works this way and you are allowed to chain transactions. It will allow you to spend a utxo that only exists in the mempool.

evaluateTransaction does not currently allow using utxos that only exist in the mempool. This prevents chaining of smart contract transactions while keeping optimal costs.

Why is it a good idea?

We should be able to chain transactions that are smart contracts and at the same time, optimize costs.

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

It's possible to cache the result of a previous call to evaluateTransaction that runs a similar smart contract and uses the same number and shape of input utxos. This is a fragile approach in that there could always be something that throws off the memory/steps calculation.