Google Apps Script:
Using an interactive shell (REPL)

How to:

Google Apps Script, a cloud-based scripting language for automating tasks across Google products, doesn’t have a built-in REPL tool similar to those in languages like Python or JavaScript’s Node.js. However, you can simulate a similar experience using the Apps Script Editor’s logging and debugging features or by setting up an external environment. Here, we focus on creating a makeshift REPL within the Apps Script editor.

1. Creating a makeshift REPL function:

function myREPL() {
  var input = Logger.log('Enter your expression: ');
  try {
    var result = eval(input);
    Logger.log('Result: ' + result);
  } catch(e) {
    Logger.log('Error: ' + e.message);
  }
}

Since direct user input isn’t feasible in the same manner as a traditional REPL in the Apps Script environment, you can modify the input variable manually and run myREPL() to test expressions.

2. Sample Code Execution:

Let’s say you wish to evaluate 2+2. You would modify the myREPL function as follows:

function myREPL() {
  var input = '2+2'; // Manually enter your expression here
  // The rest remains the same...
}

After running myREPL(), check the Logs (View > Logs) for the output, which should read something like:

[20-xx-xxxx xx:xx:xx:xxx] Enter your expression:
[20-xx-xxxx xx:xx:xx:xxx] Result: 4

3. Debugging with Logger:

For more complex debugging, intersperse Logger.log(variable); within your code to print variable states, helping you understand the flow and intermediate states of your scripts.

Deep Dive

The concept of a REPL is deeply ingrained in the history of computing, stemming from the time-sharing systems of the 1960s which allowed for interactive sessions. Languages like Lisp thrived in this environment, as the REPL was critical for their iterative development process. In contrast, Google Apps Script, emerging much later, is designed primarily for the web, focusing on automating tasks within Google’s suite over iterative, console-based programming.

Google Apps Script does not traditionally support real-time, interactive coding sessions out of the box due to its cloud-based nature and web app deployment focus. Its execution model revolves around functions triggered by web events, time-driven triggers, or manual invocation within the environment, rather than instant feedback loops provided by a REPL.

While the makeshift REPL and debugger within the Apps Script Editor offer some level of interactivity, they do not fully replicate the immediate feedback and efficiency of traditional REPLs found in many programming languages. Developers looking for a more authentic REPL experience with Google technologies might explore external JavaScript environments or Node.js with Google’s APIs. These can provide a more responsive and interactive coding session, albeit requiring more setup and potentially stepping outside the direct Apps Script environment.