GitHub - federicotdn/pimacs: Pimacs

Summary

A partial, experimental implementation of an Elisp (Emacs Lisp) interpreter, written in Go.

Project goals

• Practice Go development.
• Learn more about the Emacs internals, particularly the Elisp interpreter.
• Learn about Lisp interpreter design in general.
• Practice reading C code.
• Learn about lower level functions such as setjmp, longjmp, etc.

Usage

Assuming you have the Go compiler installed, simply use make build to compile Pimacs, and then ./pimacs to start the REPL. You can also use ./pimacs --load myfile.el to execute an Elisp script.

Note that many, many Elisp functions and macros are not implemented. You can, however, use the following (among others):

if while eval funcall apply quote function progn
unwind-protect condition-case throw signal
prin1 prin1-to-string print princ
intern read-from-string read
length equal assq memq get put plist-get plist-put nconc
null symbol-plist symbol-name set fset eq defalias
setcar setcdr car cdr cons list + <
current-buffer get-buffer set-buffer buffer-string insert

(and additionally, many predicate functions e.g. stringp, consp, etc.)

Note that some of these may be only partially implemented.

Examples

Set a variable and read it:

> (set 'greeting "hello")
"hello"
> greeting
"hello"

Create a function and call it:

> (fset 'twice (function (lambda (x) (+ x x))))
(lambda (x) (+ x x))
> (twice 21)
42

Try out a non-local exit:

> (catch 'test (throw 'test 123))
123

Design and general notes

In order to read about the design choices for Pimacs, how it works internally, and how it is different from Emacs' Elisp interpreter, see the design.md document.

Tests

Use make test to run the test suite.

Comment Tags

Since there is so much code to write, some functions contain tags within comments that specify what is missing or what should be done in order to consider the function implementation as complete.

• incomplete: Code implements some functionality correctly, but not 100% of what it should.
• revise: Code implements the entire functionality, but needs to be revised or re-thought.
• errors: Code is missing proper error handling.
• stub: Code does not implement any functionality yet.
• tests: Code needs to be tested using unit tests, or more tests need to be added for it.

License

Like Emacs, Pimacs is licensed under the GNU General Public License, version 3.