Launching Quil from the Command Line

UPDATE: The third section of this post, "Leveraging Multi-Arity", states that running lein run without arguments no longer works after adding &args to main. This is because this syntax is incorrect. To be variadic, there should be a space after the ampersand: & args. This allows for both lein run and lein run gui to work properly without needing multi-arity.

Also, there's a better way to launch Quil than using load-file, as discussed in this post.

Programmatically Launching Quil

This week I'm adding a GUI to my tic-tac-toe application. It needs to launch as a result of a terminal command and not as the result of a prompt from inside the terminal version of the game. All previous terminal functionality needs to stay intact.

Since every time I've launched Quil it's been by evaluating the Quil file from inside my IDE, the first thing I set out to do is figure out how to launch Quil from inside the code. Since Quil automatically launches when the file is evaluated, this was relatively easy using load-file. By calling load-file and passing in the filepath of the Quil file as a string starting from the src directory, I was able to get Quil to launch from the code.

Adding Arguments to Main

Next was figuring out how to do this as the result of a terminal command without first launching the terminal-based version of the game. Since lein run calls -main, it's possible to pass arguments to -main by passing them as arguments to lein run.

To get this working, I first needed to make -main take an argument, otherwise passing an argument to lein run would result in an "incorrect arity" error. To allow for a variety of argument counts to be passed in, I added a variadic parameter [&args]. Now if I type lein run gui, the value of &args will be the string "gui". This now means I can add this to -main:

(let [gui (if (= "gui" &args) 
            (do (load-file [filepath as string]) true) 
            false)] [fn body])

Now the variable gui will be set to true if I type lein run gui and Quil we be launched in the process.

Leveraging Multi-Arity

Now that -main requires arguments, I can't simply type lein run to run the terminal-based version of the game anymore. I could simply make it so the user has to type in something like "terminal" after lein run to specify that they want the terminal version of the game, but that's changing previous functionality in order to implement new functionality.

Instead, I used multi-arity to allow -main to not require arguments. If called without arguments, it sets gui to false and doesn't launch Quil. Problem solved!