# LISP 1.5 implemented in PLASMA

LISP interpreted on a bytecode VM running on a 1 MHz 6502 is going to be sssllllooooowwwww. So I called this implementation DRAWL in keeping with the speech theme. DRAWL represents an exploration REPL language for the PLASMA environment. It isn't meant to be a full-blown programming language, more of an interactive sandbox for playing with S-expressions.

## Missing features of LISP 1.5 in DRAWL

- Number values are limited to 32 bit integers, no floating point
- General recursion. The 6502 architecture limits recursion (but see tail recursion below), so don't expect too much here
- Arrays not implemented

However, the code is partitioned to allow for easy extension so some of these missing features could be implemented.

## Features of DRAWL

- 32 bit integers and basic math operators. Hey, better than you probably expected
- Tail recursion handles deep recursion. Check out [loop.lisp](https://github.com/dschmenk/PLASMA/blob/master/src/lisp/loop.lisp)
- Fully garbage collected behind the scenes
- Optionally read LISP source file at startup
- The PROG feature now present!

LISP is one of the earliest computer languages. As such, it holds a special place in the anals of computer science. I've always wanted to learn why LISP is held in such high regard by so many, so I went about learning LISP by actually implementing a LISP interpreter in PLASMA. PLASMA is well suited to implement other languages due to its rich syntax, performance and libraries.

## Links

Here are some links to get you started.

LISP 1.5 Manual: https://archive.org/details/bitsavers_mitrlelisprammersManual2ed1985_9279667

Video showing DRAWL in action: https://youtu.be/wBMivg6xfSg

Preconfigured PLASMA ProDOS boot floppy for DRAWL: https://github.com/dschmenk/PLASMA/blob/master/images/apple/DRAWL.po