aquavm/README.md

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# AquaVM

AquaVM executes compiled [Aqua](https://github.com/fluencelabs/aqua), i.e., Aqua Intermediate Representation (AIR) scripts, and plays an integral part in the implementation of the Fluence peer-to-peer compute protocol. Specifically, AquaVM allows expressing network choreography in scripts and composing distributed, peer-to-peer hosted services. Moreover, AquaVM plays a significant role in facilitating *function addressability* in the Fluence network. Figure 1.

**Figure 1: Stylized AquaVM And AIR Model**

<img alt="AquaVM & AIR model" src="images/aquavm_air_model.png" />  

Since AquaVM compiles to Wasm, it can run in both client, such as browsers and nodejs apps, and server environments.

## AquaVM: Interpreter Execution Model

AquaVM's execution model facilitates Fluence protocol's data push model implemented as a *particle*, i.e., a smart packet comprised of data, AIR, and some metadata. In this context, AquaVM can be viewed as a pure state transition function that facilitates particle updates, which includes state management of particle data by taking previous and current state to produce a new state and an updated list of peers and call requests in the remaining AIR workflow. In addition to local service call execution, AquaVM handles requests from remote peers, e.g. as part of a parallel execution block, to call local services and handle the future response. See Figure 2.

**Figure 2: AquaVM Interpreter Execution Model**

<img alt="interpreter execution model" src="images/interpreter_execution_model.png"/>

In summary, the AquaVM execution model handles the topological hops for simple and advanced composition patters, such as (async) parallel service execution on one or multiple peers.

## Aquamarine Intermediate Representation (AIR): IR For P2P Systems

AIR scripts control the Fluence peer-to-peer network, its peers and, through Marine adapter services, even resources on other (p2p) networks, such as IPFS and Filecoin, e.g., [Fluence IPFS library](https://doc.fluence.dev/aqua-book/libraries/aqua-ipfs).

### What is AIR?

- S-expression-based low-level language with binary form to come
- Consists of twelve (12) instructions with more instructions to come
- Semantics are inspired by [π-calculus](https://en.wikipedia.org/wiki/%CE%A0-calculus), [λ-calculus](https://en.wikipedia.org/wiki/Lambda_calculus) and [category theory](https://en.wikipedia.org/wiki/Category_theory)
- Syntax is inspired by [Wasm Text Format](https://developer.mozilla.org/en-US/docs/WebAssembly/Understanding_the_text_format) (WAT) and [Lisp](https://en.wikipedia.org/wiki/Lisp_(programming_language))

### AIR: Instructions

#### call

```wasm
(call <peer_id> (<service name> <service function>) [<arguments list>] <output name>)
```

- moves execution to the `peer_id` specified
- the peer is expected to host Wasm service with the specified `service name`
- the `service function` is expected to contain the specified function
- the `arguments list` is given to the function and may be empty 
- the result of the function execution is saved and returned by it's `output name`

Example:
```wasm
(call "peer_id" ("dht" "put") [key value] result)
```

#### seq

```wasm
(seq <left_instruction> <right_instruction>)
```

- executes instructions sequentially: `right_instruction` will be executed iff  `left_instruction` finished successfully

#### par

```wasm
(par <left_instruction> <right_instruction>)
```

- executes instructions in parallel: `right_instruction` will be executed independently of the completion of `left_instruction`

#### ap

```wasm
(ap <literal> <dst_variable>)
(ap <src_variable>.$.<lambda> <dst_variable>)
```

- puts `literal` into `dst_variable`
- or applies `lambda` to `src_variable` and saves the result in `dst_variable`

Example:

```wasm
(seq
    (call "peer_id" ("user-list" "get_users") [] users)
    (ap users.$.[0].peer_id user_0)
)
```

#### match/mismath

```wasm
(match <variable> <variable> <instruction>)
(mismatch <variable> <variable> <instruction>)
```

- executes the instruction iff variables are equal/notequal

Example:
```wasm
(seq
    (call "peer_id" ("user-list" "get_users") [] users)
    (mismatch users.$.length 0
        (ap users.$.[0].peer_id user_0)
    )
)
```

#### fold/next

```wasm
(fold <iterable> <iterator> <instruction>)
```

- is a form of a fixed-point combinator
- iterates through the `iterable`, assigning each element to the `iterator` 
- on each iteration `instruction` is executed
- `next` triggers next iteration
  
Example:

```wasm
(fold users user
    (seq
        (call user.$.peer_id ("chat" "display") [msg])
        (next user)
    )
)
```

#### xor

```wasm
(xor <left_instruction> <right_instruction>)
```

- `right_instruction` is executed iff `left_instruction` failed

#### new

```wasm
(new <variable>)
```

- creates a new scoped variable with the provided name (it's similar to \mu operator from pi-calculus that creates an anonymous channel)

#### fail

```wasm
(fail <variable>)
(fail <error code> <error message>)
```

- throws an exception with provided `error code` and `error message` or construct it from a provided `variable`]

Example
```wasm
(fail 1337 "error message")
```

#### null

```wasm
(null)
```

- does nothing, useful for code generation

### AIR: values
#### Scalars

- scalars are fully consistent - have the same value on each peer during a script execution
- could be an argument of any instruction
- JSON-based (fold could iterate only over array-based value)

#### Streams

- streams are CRDT-like (locally-consistent) - have deterministic execution wrt one peer
- versioned
- could be used only by call and fold instructions (more instructions for streams to come)
- could be turned to scalar (canonicalized)