Scripting Languages and Runtimes for Iroha2 Smart Contracts

Background

Currently we have Iroha Special Instructions and Expressions as a main smart contract language. Later we will call both Instructions and Expressions simply ISI.

1. Instructions - mutate global state (domains and other entities) in WSV
2. Expressions - do not mutate state (are more like mathematical calculations) and can also incorporate queries to WSV
3. Instructions can use complex input parameters in a form of Expressions.

Scripts written in ISI can be executed in 2 places:

1. As part of the transaction that user submits
2. Inside a trigger that is registered and executed on chain based on some events (see Trigger RFC) - not developed yet

Problem

Current state of ISI has several important limitations preventing it from being a fully usable smart contract language:

1. Different instruction and expressions might operate on complex values (like structs, enums), but they do not have an ability to destructure/access inner fields/variants of this complex values.
2. ISI do not have an std lib to operate Vec(s), String(s), etc.
3. In ISI it is not possible to define new structures, objects, closures, functions, modules etc. which is needed to write big programs
4. ISI can not be written in text
5. ISI do not have loops or recursion (needed for most of the programs)
6. They do not manage memory in any way

Given time all this can be solved and ISI can be turned into a fully interpreted language or compiled (JIT/or precompiled) language with a VM and assembly set. But this will take a lot of time as any language and compiler/interpreter development does and would require the team to dive heavily into this mostly new area of expertise. I would estimate about 6 month for 1 full time developer before we have a tangible prototype.

Also ISI as they are have several good important features:

1. They are relatively simple to understand and support
2. They can be easily permissioned
3. They can provide both low level and high level high performance native features

Therefore let's get to suggested solution.

Solution

It is suggested to proceed in the following way:

1. Keep ISI runtime:
   1. For simple use cases
   2. For high level features provided by Iroha natively
2. Add some other established interpreter/VM with existing scripting language such as (WASM, eBPF, Lua, Rhai)
3. Let the ISI calls be the interface between this full scripting language and our WSV (scripts will call ISI and queries to change and get information from WSV) - for universality of common interface and easy permission management

Preliminarily it is suggested to use Rust with WASM target with wasmtime runtime.

Decisions

Alternatives

Here the list of possible alternative runtimes and languages is listed with their pros and cons:

Rust - WASM

Language: Rust

Assembly: WASM

Runtime: wasmtime

Prototype: https://github.com/soramitsu/iroha2-wasm-prototype

Rust - eBPF

Needs more research

Lua

Language: Lua

Runtime: rlua

Needs more research

Rhai

Language: Rhai

Runtime: cutsom

Needs more research if deemed necessary

Concerns

Other projects developing on Iroha2 might strongly depend on this decision.

Assumptions

Projects developing on Iroha2 need a more robust scripting language

Risks

Additional Information