Femtolisp: a lightweight, robust, scheme-like lisp implementation

"...a purely symbolic gesture...

This project began with an attempt to write the fastest lisp interpreter I could in under 1000 lines of C. It snowballed from there as I kept trying to see if I could add powerful features with minimal code. At the same time I assembled a library of some of my favorite C code (by myself and others) to use as a base for a standard library. This includes ios, a replacement for parts of C's stdio that adds more flexible features.

Before you say "oh no, another lisp", consider the following: femtolisp is about 150kb, is very self-contained, and has the following features:

* vectors, strings, gensyms
* backquote
* exceptions
* printing and reading circular/shared structure
* all values can be printed readably
* prettyprinting
* hash tables
* support for directly using C data types ala Python's ctypes
* equal and ordered comparison predicates that work on circular structure
* proper tail recursion
* io and memory streams with utf8 support
* highly compatible with Scheme, including some R6RS features
* simple, well-organized, powerful API with as few functions as possible
* compacting GC

...it is fast, ranking among the fastest non-native-compiled Scheme implementations. It achieves this level of speed even though many primitives (e.g. filter and for-each) are written in the language instead of C. femtolisp uses a bytecode compiler and VM, with the compiler written in femtolisp. Bytecode is first-class, can be printed and read, and is "human readable" (the representation is a string of normal low-ASCII characters).

femtolisp is a simple, elegant Scheme dialect. It is a lisp-1 with lexical scope. The core is 12 builtin special forms and 33 builtin functions.

A primary design goal is to keep the code concise and interesting. I strive to have each concept implemented in just one place, so the system is easy to understand and modify. The result is high reliability, because there are fewer places for bugs to hide. You want a small core of generically useful features that work really well (for example, see torture.scm).

Almost everybody has their own lisp implementation. Some programmers' dogs and cats probably have their own lisp implementations as well. This is great, but too often I see people omit some of the obscure but critical features that make lisp uniquely wonderful. These include read macros like #. and backreferences, gensyms, and properly escaped symbol names. If you're going to waste everybody's time with yet another lisp, at least do it right damnit.

Another design goal is to avoid spurious novelties. Many others offering their own "shiny new" lisp dialects get carried away and change anything that strikes their fancy. These changes have no effect except incompatibility, and often make the language worse because the new design was not as carefully thought out and has not stood the test of time. For example, how does it help to remove backquote? One design changes the syntax of quote. Some systems disallow dotted lists. (I've seen all three of these.) What's the point? Implementers wave the banner of "simplicity", yet wedge in all kinds of weird implicit behaviors and extra evaluation rules.

Lately a surprising amount of FUD has been spread about proper tail recursion. I agree that not every language needs it, but I would like to refute the idea that it makes interpreters slow. Look at the "tiny" subdirectory or the "interpreter" branch to see a pure s-expr interpreter with efficient proper tail calls. All you have to do is keep track of whether you're in tail position, which can be done very cheaply. These interpreters are difficult to beat for speed, yet they have lexical scope and proper tail calls.

This project is mostly a matter of style. Look at the code and you'll understand.

This is what I do for fun, because it is the exact opposite of the kind of thing people will pay for: an obscure implementation of a programming language everybody hates."


HN discussion: https://news.ycombinator.com/item?id=22094722

#Lisp #Scheme



Mastodon for dogs. Common content warnings include "nose contact"

TIL: Babies born today will turn 18 on January 19, 2038, the first date when time becomes unrepresentable using a standard 32-bit unsigned Unix timestamp. It's not far off.

I am very tiny little spark and unique. πŸ˜‚

The main thing that pops to mind is that safety and errors are a disaster in non-R6 Scheme. But yes, parameters are the right approach to dynamic binding: dynamic extent, but lexical visibility.

I meant particularly things like dynamic-wind, but also how parameters interact with threads. It's a hard problem because in the presence of threads, dynamic-wind needs to go, and call/cc is the wrong tool. The whole core of Scheme's control flow needs rethinking.
@spectrumgomas @scheme

πŸ”€ 🐦 

Just pick 10 popular apps and learn: Nearly everything connected to an ad network is part of a massive illegal collection of user data.
EU should fine everybody involved: App authors, shops, brands, platforms, ad tech and news outlets.

♻️ a trick for super lightweight throwaway versioning for data dependencies 

imagine if 99.99% of advertisers were working on literally anything else

I have done a lil'bit of planning and I am ready to go, hopefully I will be busy-coding more than procrastinating with more thinking / planning.


I've been thinking that working on marketing for libre projects would be awesome!

Is there anyone on the fediverse I could talk to about getting a leg into that industry?

And I'm not talking about just drawings and illustrations but graphics, photoediting and videos, and finally ideas / marketing strategies.

I think I could be a great asset to projects out there.

Please share!

#linux #libre #foss #floss #opensource #libregames #mastoart #art #creative toots

Hadn't seen CNPL before, but there are many licenses out there. Basically non-commercial except for worker owned coops. The point where it falls down though is in the part about derogatory changes and the honor of the developer. Those things are undefined and would be difficult to clarify in any legal case.

Also there's the more philosophical point about non-violence not always being desirable and sometimes against the interests of workers. Consider a Paris Commune or Rojava situation.

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