A minimal lisp interpreter (+ compiler stub) that runs on the JVM
This is a very messy old project (almost 7 years old at the time of writing).
I will introduce it somewhat: To begin with: the main files to look at is
ljsp.java. The main file for bootstrapping the lisp environment is
stuff.ljsp. If you want to have a look at how to instantiate and
interact with java objects from within LJSP see: java.ljsp.
There are a lot of .j (jasmin) files that are committed. In fact most
of these are actually compilation output (see: compile.ljsp) and
commiting them to git is a bit ugly, but as some are hand-generated
mock-ups or tests of future plans for the compiler I elected to simply
commit all of them.
Some keywords for lispers: This is a lisp-1 (one namespace) with dynamic bindings (shallow), so watch out if you ever do any threading (it is in fact doable, if you're careful that any shared variables are treated as read-only). One design principle was to have as few primitive functions and forms as possible while keeping the interpreter reasonable performant, so e.g. let is simply implemented using lambda. Macros are first-class objects as far as the interpreter sees it (the compiler doesn't), they're simply a special sort of lambda whose return value is evaluated (so not quite fexprs, but could be used to implement them or vice versa).
(TODO: There are plans to change to use deep bindings and maybe even lexical scoping on top of that (as we then get passable environments), perhaps to the detriment of speed however.)
Some notes about the compiler: It is currently not very mature, and only supports static bindings: that is the variables in a function are only accesible to the function itself, and not to its callees as is the case with dynamic bindings. Since let is actually implemented using lambda, we get such strange results such as variable in the scope outside the let not being callable from inside it.
(TODO: If I ever get around to implementing lexical scoping in the compiler and interpreter their semantics could be mostly brought in line with each other that way.)
Simple compile ljsp.java:
make
and then:
ljsp.sh.
Or if you want to try out a graphical REPL-thingy:
listener.sh
I also implemented a very crude implementation of snake (the holes are a feature, not a bug!!). Simply type in any REPL:
(require 'snake)
(snake)