Merge pull request #352 from etherlinkcom/gelato-example

Simple example of using Gelato to automate contracts

Author: timothymcmackin

docs/tools/cross-chain-comms.md

@@ -7,3 +7,7 @@ title: Cross chain communication
 [LayerZero](https://layerzero.network/) is an interoperability protocol that connects blockchains, allowing developers to build seamless omnichain applications, tokens, and experiences.
 
 Learn more about sending messages across chains [here](https://docs.layerzero.network/v2/developers/evm/getting-started), and find the endpoint addresses already deployed [here](https://docs.layerzero.network/v2/developers/evm/technical-reference/deployed-contracts).
+
+## Gelato
+
+You can also use Gelato Web3 Functions to communicate across chains; see [Gelato](/tools/developer-experience#gelato).

docs/tools/developer-experience.md

@@ -19,3 +19,65 @@ It also helps manage transactions that are waiting for signatures.
 
 Gelato Web3 Functions supports Etherlink, which lets you automate Etherlink contracts based on off-chain activity and activity on other chains.
 For more information, see the Gelato Web3 Functions documentation at https://docs.gelato.cloud/Web3-Functions/Introduction/Overview.
+
+For example, this contract emits an event when its `sayMarco` function is called:
+
+```solidity
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+contract Marco {
+  event MarcoEvent(address indexed caller);
+
+  function sayMarco() public {
+    emit MarcoEvent(msg.sender);
+  }
+}
+```
+
+Similarly, this contract has a `hearMarco` function that emits an event when it is called:
+
+```solidity
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+contract Polo {
+  event PoloEvent(address indexed caller);
+
+  uint256 timesHeard;
+
+  constructor() {
+    timesHeard = 0;
+  }
+
+  function hearMarco() public {
+    timesHeard += 1;
+    emit PoloEvent(msg.sender);
+  }
+
+  function getTimesHeard() external view returns (uint256) {
+    return timesHeard;
+  }
+}
+```
+
+Because smart contracts cannot respond to events, these two contracts cannot interact directly.
+You can use Gelato Web3 Functions to listen for the `Marco` event and call the `hearMarco` function, even if these two contracts are on different networks.
+
+For example, you can register with Gelato at https://app.gelato.cloud and then click **Functions** and **New** to create a new function.
+
+On the New Function Task window, select the trigger, in this case **On-chain Event**.
+Gelato also supports time and block-based triggers.
+
+Select the network to monitor (such as Etherlink Testnet or Mainnet), specify the address and ABI of the contract, and the event to trigger on, as in this screencap:
+
+<img src="/img/gelato-trigger.png" alt="Setting the trigger condition for the Web3 Function" style={{width: 300}} />
+
+Then, further down, specify the action to run when the trigger happens.
+For example, to call the other contract's `hearMarco` function, click **Transaction**.
+Then, select the network and specify the address, ABI, and function to call, as in this screencap:
+
+<img src="/img/gelato-transaction.png" alt="Setting the transaction to run when the trigger happens" style={{width: 300}} />
+
+Now when the first contract emits the event, Gelato calls the second contract.
+These contracts can be on the same chain or different chains.