Hello World

This is the most basic lua smart contract to store and retrieve states in Meey. You can save a name on the blockchain with the contract call function. And you can print ‘hello …’ with the query function.

-- Define global state variables
state.var {
  Name = state.value(),
  My_map = state.map()
}

-- Initialize the state variables
function constructor()
  -- a constructor is called only once at the contract deployment
  Name:set("world")
  My_map["key"] = "value"
end

-- Update the name
-- @call
-- @param name          string: new name
function set_name(name)
  Name:set(name)
end

-- Say hello
-- @query
-- @return              string: 'hello ' + name
function hello()
  return "hello " .. Name:get()
end

-- register functions to expose
abi.register(set_name, hello)

This is explained based on using cli. Variables used in this example are

• Account to deploy and execute a contract: AmPPCH5aMeHnaBPJ782UynpdFa612d8runz2zY83P4AcPHqTrhqL

• Cli commands in this page need a meeysvr with enable personal feature

Check Account and Balance

First, you need an account with enough balance to deploy and execute smart contracts. (If you don’t) Import or Unlock Account to meey server.

Compile Contract

Copy above code and save it to a file (e.g. helloword.lua). And Compile using the meeyluac compiler

./bin/meeyluac --payload lua_file_location.lua

./bin/meeycli contract deploy AmPPCH5aMeHnaBPJ782UynpdFa612d8runz2zY83P4AcPHqTrhqL --payload 37mGLDoCPNDQw7HbCG5WPfcM3E3cLhqhgE2V2UJK

Get receipt of contract

Look up the actual contract address with the transaction ID above.

./bin/meeycli receipt get DyJg7jkw7AUT9ZNWyBUhwkR56V2E2HhZMGRSexamsUcJ
{
 "BlockNo": 1745,
 "BlockHash": "9NifJDJSTU9ibXsabRbr1VNxs2YeU6gC6ZMeNbAmCw8Z",
 "contractAddress": "AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB",
 "status": "CREATED",
 "ret": {},
 "txHash": "DyJg7jkw7AUT9ZNWyBUhwkR56V2E2HhZMGRSexamsUcJ",
 "txIndex": 0,
 "from": "AmPPCH5aMeHnaBPJ782UynpdFa612d8runz2zY83P4AcPHqTrhqL",
 "to": "",
 "feeUsed": 4080000000000000,
 "gasUsed": 0,
 "feeDelegation": false,
 "events": []
}

If the status is not ‘CREATED’, it may not be included in the block yet, or there may be an error. Wait a while until the transaction is included in the block. Or check the server’s error log.

Get ABI of contract

Look up ABI of contract with the contract address above.

./bin/meeycli contract abi AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB
{
 "version": "0.2",
 "language": "lua",
 "functions": [
  {
   "name": "hello"
  },
  {
   "name": "set_name",
   "arguments": [
    {
     "name": "name"
    }
   ]
  },
  {
   "name": "constructor"
  }
 ],
 "state_variables": [
  {
   "name": "Name",
   "type": "value"
  },
  {
   "name": "My_map",
   "type": "map"
  }
 ]
}

Query Initial State

You can query the generated contract in the following way.

./bin/meeycli contract query AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB hello

You can see that the name ‘world’ assigned by the constructor is output.

Call Contract

You can change the name recorded in the block chain as follows:

./bin/meeycli contract call AmPPCH5aMeHnaBPJ782UynpdFa612d8runz2zY83P4AcPHqTrhqL AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB set_name '["meeychain"]'

Query Changed State

If you look at the results again, it has changed.

./bin/meeycli contract query AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB hello

Query contract variable with merkle proof

Value

./bin/meeycli contract statequery AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB Name --compressed

Map

./bin/meeycli contract statequery AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB My_map key --compressed

Array

./bin/meeycli contract statequery AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB array_name array_index --compressed

By default, the returned state is the one at the latest block, but you may specify any past block’s state root.

./bin/meeycli contract statequery AmhTVMdngSCs3xJ5XLAZHm8MGfAdnsNEvWvtpBhRnVky4fbnLZFB var_name --root "9NBSjkcNTdE5ciBxfb52RmsVW7vgX5voRsv6KcosiNjE"