This is a small Lisp interpreter in Dart. In 2015 (H27), I wrote the first version in Dart 1.9. It had been presented under the MIT License at http://www.oki-osk.jp/esc/dart/lisp.html (broken link) until the spring of 2017 (H29). In 2018 (H30), I slightly modified it to match Dart 2.0 and made the repository in GitHub.

Now in 2019 (R1), I found the old hack in Sym class

  @override int get hashCode => name.hashCode;

which had once accelerated the interpreter is effective again in Dart 2.5. So I included the hack in Sym class again. In addition, I made use of BigInt because int does not have inifinite-precision in Dart 2.0 and later.

See IMPLEMENTATION-NOTES.md for other details of the implementation.

It runs in Dart 2.5 and later.

$ dart lisp.dart
> "hello, world"
"hello, world"
> (+ 5 6)
11
> (exit 0)
$

You can give it a file name of your Lisp script.

$ dart lisp.dart examples/fib15.l
987
$

If you put a "-" after the file name, it will begin an interactive session after running the file.

$ dart lisp.dart examples/fib15.l -
987
> (fib 0)
1
> (fib 1)
1
> (fib 2)
2
> (exit 0)
$ 

There are five files ending with .l under the examples folder. These run also in Emacs Lisp and Common Lisp. You may find the Lisp in Dart comparably fast to Emacs Lisp which is written in C.

• qsort.l performs a quick sort.

$ ./lisp.dart examples/qsort.l
(1 1 2 3 3 4 5 5 5 6 7 8 9 9 9)
$ 

$ emacs -batch -l examples/qsort.l

(1 1 2 3 3 4 5 5 5 6 7 8 9 9 9)
$ 

$ clisp examples/qsort.l

(1 1 2 3 3 4 5 5 5 6 7 8 9 9 9)
$ 

• fact100.l calculates 100!.

$ ./lisp.dart examples/fact100.l 
93326215443944152681699238856266700490715968264381621468592963895217599993229915
608941463976156518286253697920827223758251185210916864000000000000000000000000
$

• fib15.l calculates Fibonacci for 15.

• eval-fib15.l calculates Fibonacci for 15 on a meta-circular Lisp evaluator.

$ ./lisp.dart example/eval-fib15.l
987
$ 

• eval-eval-fib15.l calculates Fibonacci for 15 on a meta-circular Lisp evaluator on a meta-circular Lisp evaluator.

The examples of eval-fib15.l and eval-eval-fib15.l are inspired by https://github.com/zick/ZickStandardLisp.

There is one more example:

• interp_in_isolate.dart runs a Lisp interpreter in another isolate of Dart. You can embed an interpreter within your Flutter app in the same way.

$ dart examples/interp_in_isolate.dart
=> 11
=> 1
=> (1)

This is under the MIT License. See lisp.dart.