LispE: Lisp Interpreter with Pattern Programming and Lazy Evaluation | Hacker News Reader

LispE: Lisp Interpreter with Pattern Programming and Lazy Evaluation

github.com

119 pointsPaulHoule25 comments

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> LispE provides an alternative to parentheses with the composition operator: "."

That is a... Choice.

Breaking the pair operator in favour of something new.

Yeah, that's pretty unclean on two aspects: breaks pairs, and breaks the orthogonality of s-expressions

A simple macro would've sufficed, say:

  (compose
    sum
    (numbers 1 2 3))

I don't think it's too bad orthogonality wise, though it is a bit weird to introduce infix notation. It would almost make more sense to write

((. sum numbers) (1 2 3))

Your approach is better on a mathematical sense, yes. That’s how Haskell does it.

schemers used a good old `compose` instead of a dedicated syntax

I'm not too fond of adding extra syntax or infix operators to Lisps but I have been thinking lately if maybe some limited form of infix macros could be useful, mainly in binding forms and such. E.g anaphoric ifs were a thing in the past for binding conditional expression's value; currently the preferred method seems to be if-let, or when-let and maybe unless-let too, and of course also the let* variants. And for completeness one might also need cond-let with its own different semantics. Oh, and maybe letrec and a few others too. But at that point it might make sense to come up with some kind of define-let-form macro facility to deal with the general pattern.

But all that gives me a nagging feeling that maybe traditional Lisp macros don't really compose that well? So as a band-aid I had the idea to introduce special infix macros so one could for example do "(if (expr as: var) (something-something var))", or maybe "(something-something var where: var expr)" and so on. I'm not sure what the exact semantics should be though, especially with the as: form. It's probably just a result of doing too much Smalltalk lately, but out of all the "let's fix lisp's syntax" ideas I don't think I have seen exactly this one before, so that's something I guess. (As an alternative we could also of course just replace the lambda form with something less verbose so one could "(if expr [var | something-something var])" and then make the conditionals regular functions, or even generic ones specialized on booleans. Or maybe I'll just get back to hacking my init.el for now and try to cleanse my mind of these impure thoughts.)

SRFI-105 is an infix syntax that composes well, and is supported by most Schemes.

Its enabled by default with Guile, for example.

    (+ 1 2 {10 * 2} 6)

https://srfi.schemers.org/srfi-105/

and beside multiple-args, there's the usual threading macros

    (-> [1 2 3] f g)

It's not too bad. I like it! Haskell uses "$" to do the same thing.

Well, you could use $ in Lisp, too. Thats a standard valid symbol, that doesn't have a builtin meaning.

Technically $ means something slightly different, it is more somilar to putting parentheses around the right half of the expression. For function composition it uses the same '.' .

After programming in Common Lisp for a few years (a long time ago) and then later on having a brief period where I was fond of Python, I did also become fascinated with the concept of lisps where indentation replaces parenthesis such as Wisp:

https://www.draketo.de/software/wisp

Mind you - I usually end up concluding that Lisp syntax is actually pretty good as it is...

I've always been tempted with wisp. Ever since I saw SRFI-110. Love the concept.

I just never quite manage to grasp the new syntax.

There's a new one, pretty good, resembling Python/Julia syntax, check it out! https://moonli-lang.github.io/

    defun multiply-thrice(x):
      print(x * x * x)
    end

    multiply-thrice(23)

It all ends up like YAML. Thanx but I'd rather take the parens any day.

I honestly would've prefered someone try and turn xml into a lisp, at least that has a cool hack value

They’ve got a page on that. They did away with linked lists and chose to represent them as vectors. With some of the usual stuff you see going on under the hood in this style of list on imperative languages, like pre-allocating a little room for growth.

I can’t opine on whether that’s a good choice. But I will observe two things: first, singly linked lists aren’t as great on modern computing architectures as they were 50 years ago. Locality of reference matters a lot more now. And second, both Hy and Clojure abandoned the traditional focus on dotted pairs, and in both cases I found it was fine. (Disclaimer, I didn’t spend a whole lot of time with Hy.)

Uh... Most Schemes don't use linked lists under the hood. That doesn't impact the syntax, just the implementation.

Guile uses vectors, for example. [0]

Chicken... Is Cheney, so your list disappears entirely, half the time.

Gambit uses vectors. [1]

[0] https://www.gnu.org/software/guile/manual/html_node/Cheaper-...

[1] https://github.com/gambit/gambit/blob/master/gsc/_back.c#L11...

I agree that there is maybe too much potential for confusion with that, but is the dot operator (or read syntax?) actually used that much these days?

Personally I have mostly sometimes used it with Emacs Lisp, but in general relying too much on plain cons cells and cadring down the cars of their cddars feels like a code smell to me and if I need a pair I can always just use cons? As the (only, I think?) infix operator in traditional lisps it has always felt extra-ordinarily useless to me (outside of Schemes use of it lambda lists), but maybe I'm just missing something.

Pairs are used by about 3-quarters of the standard library of Scheme, so I really would not consider its use to be a code smell.

You should be using the pairs when using make-hash, for example.

Cons also doesn't always return a pair. Its main purpose is for prepending to a list. Only when "the second argument is not empty and not itself produced by cons" does it produce a pair.

Which means '(a . b) is clearer code in intent, than (cons a b).

Good points. I don't think pairs are a code smell when used reasonably in situations where a pair of two values makes sense, like in your make-hash example. Ideally though I'd like to have a real, distinct (immutable) pair/association type separate from the cons/list and maybe use the dot syntax for that instead.

Deeply nested pair & list constructs that need to be unpacked with complex car/cdr combinations is what IMHO gets messy and I take the appearance of cddar & co in code as a sign that I should start thinking about using proper data structures.

A distinct and immutable pair is... A pair.

    (eq? (pair? '(A . B)) #t)

    (eq? (pair? (list 1 2 3)) #f)

But agree you probably want list-ref instead of cddr and friends.

I think you need something like it in order to have a print representation of a cons cell whose cdr is not a cons-or-nil. And it's nice if your print representations are readable.

Whoa I never expected to see a lisp repository from Naver

I knew a company, StorySense, and their main product WhatsTheNumber used Lisp (maybe Scheme?) for the main logic in the back end. One of the founders previously worked at MIT Media Lab. Interestingly enough their competitor, Whoscall, was acquired by Naver. I wonder if they also used Lisp and if LispE is related to that product at all.

https://www.cw.com.tw/article/5067306

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