Show HN: A Lisp interpreter in C# 7 | Hacker News Reader

Show HN: A Lisp interpreter in C# 7

github.com

30 pointssuzuki7 comments

Despite its humble size, this is a pretty sophisticated Lisp implementation. Not that one that can only do some additions, but also macros and stuff.

Kudos for doing the Lisp thing right.

UPDATE: Took one more look, this implementation is really impressive. It does stuff like 'defmacro', the whole code is just 1400 lines of C#. Never saw anything that effective in terms of functionality per line of code till this day. Impressive, very impressive. Also thanks for sharing.

Thank you. This Lisp is a translation of my other Lisp in 1200 lines of Dart (https://github.com/nukata/lisp-in-dart), which is, in turn, a digest or refinement of my old L2Lisp in Java (https://github.com/nukata/l2lisp-in-java). I did my best to optimize it for C# 7.

Good job Mr. Suzuki. You effort on C# 7 optimization shows, the result is clean and professional.

Regarding the speed of .NET implementation, it can be improved by leveraging LINQ expressions trees. In this way, one can achieve a good interpreter/JIT combo. The compiled code produced by LINQ expression trees is discardable. So you can temporarily cache it for frequent Lisp expressions (this gives JIT performance), and then discard rarely used parts of it (this gives a flexibility of an interpreter).

I'm myself in a Scheme camp of Lisp, but I love your implementation. This is the cleanest one I saw in years.

Neat! One thing to mention, I would remove most of the benchmarks, and include only clisp, sbcl (I guarantee you this one is the fastest), clozure cl (ccl), and abcl.

I wonder if it might be unfair to include the byte-compiled results (with .fast and .elc files) of CLISP and Emacs Lisp to the table.

Neat work! Also good demonstration of new C# 7.0 features.

Thank you. I appreciated especially the pattern matching feature of C# 7 while programming the interpreter. For example:

        /// <summary>Evaluate a Lisp expression in an environment.</summary>
        public object Eval(object x, Cell env) {
            try {
                for (;;) {
                    switch (x) {
                    case Arg xarg:
                        return xarg.GetValue(env);
                    case Sym xsym:
                        try {
                            return Globals[xsym];
                        } catch (KeyNotFoundException) {
                            throw new EvalException("void variable", x);
                        }
                    case Cell xcell:

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