Layer 2 built-in support

[KtorZ]

Building up on the new V3 syntax:

validator my_validator(arg1: Whatever) {
  spend (datum: Option<Datum>, redeemer: Redeemer, utxo_ref: OutputReference, ctx: Transaction) {
    ...
  }

  mint (redeemer: Redeemer, policy_id: PolicyId, ctx: Transaction) {
    ...
  }

  else(_) { fail }
}

We could imagine augmenting the syntax to support custom purposes; and use that syntax to define Cardano's purposes themselves. The definition for Cardano would be implicitly provided when unspecified, and would be equivalent to:

validator my_validator(arg1: Whatever) for Cardano {
  ...
}

The idea would be to have the validator's purpose names be the (lowercased) variants of a defined type + the else branch:

purpose Cardano = 0 {
  Spend(...)
  Mint(..)
  Publish(..)
  Vote(..)
}

The syntax for defining new purpose should also include ways of specifying the constructor index for the script context corresponding to that purpose (the Cardano ledger currently uses 0).

So for example, if we imagine a layer 2 "Gummiworm" associated with the constructor 1, we could have:

purpose Gummiworm = 1 {
  Swallow(...)
  Scream(..)
  Shout(..)
}

validator my_validator(arg1: Whatever) for Gummiworm {
  swallow(..) { ... }
  scream(..) { .. .} 
  else(..) { ... }
}

Notice that the names of the validator is the same, such that it compiles to a single program (single hash) across all layers.