Whitepaper - Ethereum Classic With Cover

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Ethereum Classic Documentation, Release 0.1 1.7.2 Contracts What is a contract? A contract is a collection of code (its functions) and data (its state) that resides at a specific address on the Ethereum blockchain. Contract accounts are able to pass messages between themselves as well as doing practically Turing complete computation. Contracts live on the blockchain in a Ethereum-specific binary format called Ethereum Virtual Machine (EVM) bytecode. Contracts are typically written in some high level language such as Solidity and then compiled into bytecode to be uploaded on the blockchain. See also: Other languages also exist, notably Serpent and LLL, which are described further in the Ethereum high level languages section of this documentation. Dapp development resources lists the integrated development environments, developer tools that help you develop in these languages, offering testing, and deployment support among other features. Ethereum high level languages Contracts live on the blockchain in an Ethereum-specific binary format (EVM bytecode) that is executed by the Ethereum Virtual Machine (EVM). However, contracts are typically written in a higher level language and then compiled using the EVM compiler into byte code to be deployed to the blockchain. Below are the different high level languages developers can use to write smart contracts for Ethereum. Solidity Solidity is a language similar to JavaScript which allows you to develop contracts and compile to EVM bytecode. It is currently the flagship language of Ethereum and the most popular. • Solidity Documentation - Solidity is the flagship Ethereum high level language that is used to write contracts. • Solidity online realtime compiler • Standardized Contract APIs • Useful Ðapp Patterns - Code snippets which are useful for Ðapp development. Serpent Serpent is a language similar to Python which can be used to develop contracts and compile to EVM bytecode. It is intended to be maximally clean and simple, combining many of the efficiency benefits of a low-level language with ease-of-use in programming style, and at the same time adding special domain-specific features for contract programming. Serpent is compiled using LLL. • Serpent on the ethereum wiki • Serpent EVM compiler LLL Lisp Like Language (LLL) is a low level language similar to Assembly. It is meant to be very simple and minimalistic; essentially just a tiny wrapper over coding in EVM directly. • LIBLLL in GitHub • Examples of LLL 1.7. Contracts and Transactions 79
Ethereum Classic Documentation, Release 0.1 Mutan (deprecated) Mutan is a statically typed, C-like language designed and developed by Jeffrey Wilcke. It is no longer maintained. Writing a contract No language would be complete without a Hello World program. Operating within the Ethereum environment, Solidity has no obvious way of “outputting” a string. The closest we can do is to use a log event to place a string into the blockchain: contract HelloWorld { event Print(string out); function() { Print("Hello, World!"); } } This contract will create a log entry on the blockchain of type Print with a parameter “Hello, World!” each time it is executed. See also: Solidity docs has more examples and guidelines to writing Solidity code. Compiling a contract Compilation of solidity contracts can be accomplished via a number of mechanisms. • Using the solc compiler via the command line. • Using web3.eth.compile.solidity in the javascript console provided by geth or eth (This still requires the solc compiler to be installed). • The online Solidity realtime compiler. • The Meteor dapp Cosmo for building solidity contracts. • The Mix IDE. • The Ethereum Wallet. Note: More information on solc and compiling Solidity contract code can be found here. Setting up the solidity compiler in geth If you start up your geth node, you can check which compilers are available. > web3.eth.getCompilers(); ["lll", "solidity", "serpent"] This command returns an array of strings indicating which compilers are currently available. Note: The solc compiler is installed with cpp-ethereum. Alternatively, you can build it yourself. If your solc executable is in a non-standard location you can specify a custom path to the solc executable using th --solc flag. $ geth --solc /usr/local/bin/solc Alternatively, you can set this option at runtime via the console: 80 Chapter 1. Contents
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