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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.
  • Learn about the general challenges found when creating a text editor.

Usage

Assuming you have the Go compiler installed, simply use make build to compile Pimacs, and then ./pimacs to start the REPL.

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

intern read-from-string read load eval funcall apply progn prog1 cond
setq and or if while quote function defconst let let* catch
unwind-protect condition-case throw signal prin1 print princ
prin1-to-string null sequencep consp listp symbolp stringp
number-or-marker-p char-or-string-p integerp numberp bufferp
characterp char-table-p vectorp boundp fboundp makunbound fmakunbound
car cdr car-safe cdr-safe setcar setcdr symbol-plist symbol-name set
fset symbol-value symbol-function eq defalias + < bare-symbol cons
list length equal eql assq assoc memq get put plistp plist-get plist-put
nconc provide nreverse reverse require nthcdr nth mapcar buffer-string
insert current-buffer set-buffer get-buffer buffer-name buffer-list
get-buffer-create read-from-minibuffer getenv-internal recursive-edit
make-char-table char-table-range set-char-table-range
char-table-parent set-char-table-parent multibyte-string-p %

Note that some of these may be only partially implemented, or be a stub/placeholder.

Examples

Set a variable and read it:

> (setq 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

Create a vector of integers:

> (setq vec [1 2 3 4])
[1 2 3 4]
> (vectorp vec)
t

Use backquotes:

> (setq lst '(2 3 4))
(2 3 4)
> `(1 ,@lst 5 6)
(1 2 3 4 5 6)

Create a multibyte string:

> (setq s "ñandú")
"ñandú"
> (multibyte-string-p s)
t

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.

Similar projects

Check out Rune, a re-implementation of Emacs from scratch using Rust.

License

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