3. working with the copilot

While it is possible to simply run finished programs as we just did with the hello.alv example, alv is a livecoding language, which means that it is designed so that programs can be written interactively while they are already running. To see how this works, let’s re-write the hello.alv example step-by-step.

First you will need an empty file to start from. Open a new file in your preferred text editor and save it as test.alv. Before adding any code, start the copilot (see the last page on the two ways of doing that).

$ alv test.alv
changes to files: test.alv

You should see a note indicating that alv processed the file. The note will show up in the upper pane labelled eval (in the GUI), or colored green (in the terminal). This marks the message as an eval-time message, meaning that the message was printed as a direct response to the file changing or being loaded the first time. Other messages that might print to the eval section are things like errors in your program, and one-time debugging messages.

Now that the copilot is running, whenever you change test.alv and save it, the copilot will reload it and execute your new code. When you are done, you can stop the copilot at any time by closing the GUI window or pressing ^C (control-C) in the terminal.

Let’s start with a simple operator, print: print is used simply to print messages to the copilot console. Enter the following in your file and save it:

(print "hello world!")

As soon as you save the file, you should notice two things happening:

The copilot will print two new lines:
```
changes to files: hello.alv
hello world!
```
In the first line, it notifies us that the file has changed. In the second line, you can see the output from the print expression.
The copilot will make a small modification to your file. Depending on the editor you are using, this may either result in you seeing the modification immediately, or a notice appearing that offers the option to reload the file. If it is the latter, confirm the notification to accept the changes. If there is an option to do so, you may want to configure your editor to always reload the file automatically.

The code should now look like this:

([1]print "hello world")

The [1] that the copilot added to your expression is that expression’s tag. In alv, every expression has a tag that helps the copilot to identify the individual expressions as you make changes to your code. The copilot will make sure that all expressions are tagged by adding missing tags when you save the file, but you have to watch out not to duplicate a tag when copying and pasting code. When you duplicate code that already has tags, you can either manually change the tags to be unique, or simply delete the whole tag (including the square brackets) and let the copilot generate a new one for you the next time you save the file.