erc777.sol

//SPDX-License-Identifier: GPL-v3
pragma solidity ^0.8.0;
pragma experimental SMTChecker;

interface IERC777Recipient {
	function tokensReceived(
		address from,
		address to,
		uint256 amount
	) external;
}

interface IERC777Sender {
	function tokensToSend(
		address from,
		address to,
		uint256 amount
	) external;
}

contract ERC777 {
	mapping (address => uint256) balances;
	uint totalSupply;
	bool lock;

	function deposit(uint _amount) public payable {
		require(_amount == msg.value);
		require(msg.value > 0);
		balances[msg.sender] += msg.value;
		totalSupply += msg.value;
	}

	function withdraw(uint _amount) public {
		require(_amount > 0 && _amount <= balances[msg.sender]);
		payable(msg.sender).transfer(_amount);
		balances[msg.sender] -= _amount;
		totalSupply -= _amount;
	}

	function transfer(address _to, uint _amount) public {
		require(msg.sender != _to);
		require(_amount > 0);
		require(balances[msg.sender] >= _amount);
		uint preSupply = totalSupply;

		balances[msg.sender] -= _amount;
		balances[_to] += _amount;

		//IERC777Sender(msg.sender).tokensToSend(msg.sender, _to, _amount);
		//IERC777Recipient(_to).tokensReceived(msg.sender, _to, _amount);

		assert(totalSupply == preSupply);
	}
}