Given the significant restrains of the NES hardware, making any game is difficult enough, let alone one with as much content as What Remains. Only by creating useful subsystems to hide and manage this complexity were we able to work as a team to complete the game.

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Any real-time game more complicated than Tetris has at its core an “entity system”. This is the functionality that allows for multiple independent actors which act simultaneously and are responsible for their own state. Though What Remains is by no means an action game, it still has screens full of independent actors with complex behavior: animating and drawing themselves, checking for collisions, and triggering dialog.

When reading the README file of their github it is possible to see how "impure" pragmatic decisions were made like for loops and not supporting proper recursion. I wish there would be more projects like this one porting lisp runtimes to more and more hardware.

What they didn’t do is what many people might think are table stakes with Lisp: writing a garbage collector, writing a runtime, supporting lambdas, and so on. Those are unreasonable asks for 2K RAM on a 6502. I wouldn’t say they wrote a bonafide Lisp, but they made use of many ideas of Lisp successfully to write a game that is very surprisingly readable while not being too abstract over assembly.

...a custom language was developed in tandem with the game. Co2 is a Lisp-like language, built on Racket Scheme, which compiles into 6502 assembly. This language was originally started by Dave Griffiths to build the What Remains demo, and I decided to stick with it for the full project.

Co2 makes it possible to write inline assembly when needed, but also has higher-level facilities that make certain tasks easier. It implements local variables that are efficient both in terms of ram consumption and access speed[+]. It has a very simple macro system that helps write readable, and also efficient code[+]. Most importantly, it makes representing data directly in the source a lot easier, thanks to lisp’s homoiconicity.