Move Language

Move is a new programming language developed to provide a safe and programmable foundation for the Libra Blockchain.

Organization

The Move language directory consists of five parts:

• The virtual machine (VM), which contains the bytecode format, a bytecode interpreter, and infrastructure for executing a block of transactions. This directory also contains the infrastructure to generate the genesis block.

• The bytecode verifier, which contains a static analysis tool for rejecting invalid Move bytecode. The virtual machine runs the bytecode verifier on any new Move code it encounters before executing it. The compiler runs the bytecode verifier on its output and surfaces the errors to the programmer.

• The Move intermediate representation (IR) compiler, which compiles human-readable program text into Move bytecode. Warning: the IR compiler is a testing tool. It can generate invalid bytecode that will be rejected by the Move bytecode verifier. The IR syntax is a work in progress that will undergo significant changes.

• The standard library, which contains the Move IR code for the core system modules such as LibraAccount and LibraCoin.

• The tests for the virtual machine, bytecode verifier, and compiler. These tests are written in Move IR and run by a testing framework that parses the expected result of running a test from special directives encoded in comments.

How the Move Language Fits Into Libra Core

Libra Core components interact with the language component through the VM. Specifically, the admission control component uses a limited, read-only subset of the VM functionality to discard invalid transactions before they are admitted to the mempool and consensus. The execution component uses the VM to execute a block of transactions.

Exploring Move IR

• You can find many small Move IR examples in the tests. The easiest way to experiment with Move IR is to create a new test in this directory and follow the instructions for runnning the tests.
• Some more substantial examples can be found in the standard library. The two most notable ones are LibraAccount.mvir, which implements accounts on the Libra blockchain, and LibraCoin.mvir, which implements Libra coin.
• The four transaction scripts supported in the Libra testnet are also in the standard library directiory. They are peer-to-peer transfer, account creation, minting new Libra (will only work for an account with proper privileges), and key rotation.
• The most complete documention of the Move IR syntax is the grammar. You can also take a look at the parser for the Move IR.
• Check out the IR compiler README for more details on writing Move IR code.

Directory Organization

├── README.md          # This README
├── bytecode_verifier  # The bytecode verifier
├── functional_tests   # Testing framework for the Move language
├── compiler           # The IR to Move bytecode compiler
├── stdlib             # Core Move modules and transaction scripts
├── test.sh            # Script for running all the language tests
└── vm
    ├── cost_synthesis # Cost synthesis for bytecode instructions
    ├── src            # Bytecode language definitions, serializer, and deserializer
    ├── tests          # VM tests
    ├── vm_genesis     # The genesis state creation, and blockchain genesis writeset
    └── vm_runtime     # The bytecode interpreter