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@@ -1,3 +1,40 @@ # LISP and beyond from bare metal It's `eval`s all the way up + +## Background + +In 2022 I wrote a LISP interpreter in PDP-11 assembly, +hand-translated it into machine code, +and toggled it in directly to the front panel +of my PhD advisor's PiDP-11. +I kept as close as possible +to the system described in John McCarthy's original paper +(other than fixing the known bug in `eval`). + +This is that project. +The original plan involved using it +to bootstrap an even better interpreter, +but I lost some momentum +when I realized +the thing I created had dynamic instead of lexical scoping, +and also when +the PiDP-11 got turned off +and lost its emulated memory contents. + +I gave a little presentation on it anyway; +the slides for that can be found +[here](https://jacquescomeaux.xyz/lisp-from-scratch.pdf). +In short, S-Functions manipulate S-Expressions, +but descriptions of S-Functions *are* S-Expressions. +`eval` is the S-Function that reads an S-Expression +which describes an S-Function, +and does the thing that that description describes. + +## Learning more + +If you want to know more +and know how to find me in real life, +please do so +and I'd be happy to talk +about any of this stuff in more detail. |