0. Evaluation

Starting Moonli either using the included binary or using VS Code will start a Read–Eval–Print Loop (REPL).

In VS Code, you will need to switch to a separate tab that contains the REPL. TODO: Elaborate more on evaluation in VS Code.

MOONLI-USER> 

A REPL is how many interactive programming languages work. It’s a simple cycle: the computer reads what you type, evaluates it (figures out what it means and runs it), prints the result, and then loops back to wait for your next command. For example, if you type defparameter x = 5 in the REPL, it evaluates it. It binds the variable x to the value 5.

MOONLI-USER> defparameter x = 5
[OUT]: x

MOONLI-USER> 

Next, if you type x, it evaluates x to return the value 5.

MOONLI-USER> x
[OUT]: 5

This loop makes programming feel conversational – you can test ideas instantly, explore code step by step, and see exactly how the language thinks and responds.

For any input, you can prevent evaluation by prefixing it with $. This is known as quote-ing.

MOONLI-USER> $x
[OUT]: x