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a lightweight, robust, scheme-like lisp implementation

branch: master

Merge pull request #12 from tluyben/master

Femtolisp works now on modern macs (fix from Julia)
latest commit 27b18d04d0
Jeff Bezanson authored
Octocat-spinner-32 attic remove and clean up some old files June 11, 2013
Octocat-spinner-32 examples remove and clean up some old files June 11, 2013
Octocat-spinner-32 lib a rename February 17, 2012
Octocat-spinner-32 llt Femtolisp works now on modern macs (fix from Julia) February 26, 2014
Octocat-spinner-32 tests fixing large int64 comparison bug March 15, 2012
Octocat-spinner-32 tiny remove and clean up some old files June 11, 2013
Octocat-spinner-32 .gitignore gitignore flisp.boot.bak June 11, 2013
Octocat-spinner-32 LICENSE moving stuff around some more February 17, 2012
Octocat-spinner-32 Makefile trying some preprocessor platform detection March 17, 2013
Octocat-spinner-32 Makefile.macosx Updated carbon path and pointer size check May 08, 2013
Octocat-spinner-32 README.md moving stuff around some more February 17, 2012
Octocat-spinner-32 aliases.scm several minor changes and additions: June 08, 2013
Octocat-spinner-32 ascii-mona-lisa moving stuff around some more February 17, 2012
Octocat-spinner-32 ascii-mona-lisa-2 moving stuff around some more February 17, 2012
Octocat-spinner-32 bootstrap.sh moving stuff around some more February 17, 2012
Octocat-spinner-32 builtins.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 compiler.lsp fix lack of error when calling builtins with the wrong number of args August 26, 2013
Octocat-spinner-32 cvalues.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 equal.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 equalhash.c moving stuff around some more February 17, 2012
Octocat-spinner-32 equalhash.h removing leading/trailing underscores from preprocessor symbols February 20, 2012
Octocat-spinner-32 flisp.boot fix lack of error when calling builtins with the wrong number of args August 26, 2013
Octocat-spinner-32 flisp.c Merge branch 'master' of github.com:JeffBezanson/femtolisp June 10, 2013
Octocat-spinner-32 flisp.h several minor changes and additions: June 08, 2013
Octocat-spinner-32 flmain.c Merge branch 'master' of github.com:JeffBezanson/femtolisp June 08, 2013
Octocat-spinner-32 iostream.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 mkboot0.lsp moving stuff around some more February 17, 2012
Octocat-spinner-32 mkboot1.lsp moving stuff around some more February 17, 2012
Octocat-spinner-32 opaque_type_template.c moving stuff around some more February 17, 2012
Octocat-spinner-32 opcodes.h removing leading/trailing underscores from preprocessor symbols February 20, 2012
Octocat-spinner-32 operators.c fixing large int64 comparison bug March 15, 2012
Octocat-spinner-32 print.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 read.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 string.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 system.lsp simpler proxy function for list builtin June 11, 2013
Octocat-spinner-32 table.c several minor changes and additions: June 08, 2013
Octocat-spinner-32 todo moving stuff around some more February 17, 2012
Octocat-spinner-32 todo-scrap moving stuff around some more February 17, 2012
Octocat-spinner-32 types.c several minor changes and additions: June 08, 2013
README.md

...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
  • and...

...it is fast, ranking among the fastest non-native-compiled Scheme implementations. It achieves this level of speed even though many primitives (like map) 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 tail call optimization. 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 TCO. 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 TCO.

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.

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