If you are creating Lisp because you want to create Lisp, like creating Lisp, want to show off creating Lisp, that obviously is not what the Law is about.

Furthermore, if you create Lisp because you know the Law, know it is inevitable, and want to avoid the caveats and missed bars by doing so explicitly, well then that also is not what the Law is about.

But if you are going about your business, focused on your independent goal, realize you need Lisp like lists, and then 250 lines of code later realize you have created a solid Lisp unintentionally? Well, congrats on falling into the trap but not getting hurt!

—

Personally, I have created both Lisp and Forth multiple times for suitable projects where I wanted some flexible runtime scripting. I am not familiar with the standard version libraries of either and don’t need them.

Minimal foundation implementations are extremely easy to create, and eliminate any dependencies or sources of mystery.

Anyone know of any other well designed mininal languages?

  template <typename Result, typename Head, typename ...Tail>
  struct Foo : Visitor {
    Result res;
    UntypedList lst; // This does not exist!
    Tail... tail;    // This is not possible!
    Foo(UntypedList l; Head hd, Tail... tl) : lst(l), tail(tl) {
      hd->accept(*this);
    }
    void visit(float *f) {
      res = Foo<Result, Tail...>(append(lst, f), tail)::res; }
    }
  };
 
  // Base case that calls the multimethod omitted.

Why can the compiler not infer the types in such an UntypedList? Why is there no car/cdr for tuples?

But what is "sufficiently" complicated? Now it's a silly statement that just doesn't pass Popper criterion: even if nobody dares to deny your program is complicated, one can always say it isn't sufficiently complicated, hence the fact it doesn't contain Lisp-interpreter disproves nothing. A man of culture wouldn't use such definitions.

You can use proc_macro::Span.line()/column() [1] to track how much whitespace there is between tokens and merge them, but the macro will have to rename them to valid Rust identities ("foo-bar" to "foo_bar") and make sure there's no collisions.

[1] https://doc.rust-lang.org/proc_macro/struct.Span.html#method...

  (deftype list-of (type)
    `(cons ,type (or null (list-of ,type))))

  (typep '(1 2 3 4) '(list-of integer))
  => T

  (deftype satisfiesp (function)
    (let (predicate)
      (cond ((symbolp function)
             (setq predicate function))
            ((functionp function)
             (setq predicate (gensym))
             (setf (symbol-function predicate) function))
            ((and (consp function) (eq (car function) 'lambda))
             (setq predicate (gensym))
             (compile predicate function))
            (t (error "~S is neither a lambda expression, function or symbol." function)))
      `(satisfies ,predicate)))

  (defvar foo 'bar)
  (typep 'bar `(satisfiesp (lambda (x) (eq x ',foo))))
  => T

Thanks for sharing your project, by the way - between this and the other one you linked, I think I know what my leisure time this weekend is going to consist of...