Hello everyone,
How’s it going?
There is now a working version of (parenscript:defpsmacro tagbody (&body body) …)), See my blog post here: "https://dapperdrake.neocities.org/faster-loops-javascript https://dapperdrake.neocities.org/faster-loops-javascript” .
This adds nestable (tagbody … (tagbody …) …)) forms as a user-land library to parenscript.
Apologies for missing documentation. It will be added gradually. Also, hosting a tarball on Neocities.org is planned in future as well as somehow getting the library into quicklisp. A name like parenscript-tagbody-go seems useful.
This code is still missing the check of *DEFINED-OPERATORS*. How is that supposed to look?
Cheers, Andrew
On May 29, 2022, at 20:24, Andrew Easton andrew@easton24.de wrote:
Hi Philipp,
That sounds like a good plan.
From my current vantage point, this seems like step three. I just got done with at step one. Step two is for me to get acquainted with the parenscript codebase.
I will get a feel the existing code base and then we can take the next steps from there.
I already cloned the git repository to my local development machine. The current commit for branch master seems to be:
commit 1fd720bc4e2bc5ed92064391b730b9d4db35462a (HEAD -> master) | Author: Vladimir Sedach vas@oneofus.la | Date: Wed Jun 17 20:29:19 2020 -0700
Regarding tail-call optimization in JavaScript: Jason Miller also recommended that. Unfortunately, I dug up information indicating that it is unsupported in Google's V8 JavaScript implementation, see [stackoverflow.com (2017)].
Quoting part of my reply to Jason for the benefit of future readers of this specific email:
[...] This seems to necessitate a (loop (case ...)) based approach, because SERIES may be used for loops with iteration counts greater than the stack size. Nevertheless, not all is lost.
PARENSCRIPT already compiles (block nil ((lambda () (return 3)))) as catch/throw correctly. Note, the call in the body of the BLOCK. So at least some dynamic ((lambda () (go ...))) calls should be compilable; hopefully all of them. Even if it only captures 70% of all use cases, that is way more than zero.
Cheers, Andrew
[stackoverflow.com (2017)], Answer by T.J. Crowder: TITLE: ES6 Tail Recursion Optimisation Stack Overflow, URL: https://stackoverflow.com/questions/42788139/es6-tail-recursion-optimisation...
On Sat, May 21, 2022 at 10:58:57AM +0200, Philipp Marek wrote:
Hi Andrew,
first of all -- how about registering on gitlab.common-lisp.net, so that you can become a developer for [1] and work with a branch using a Merge Request? It would be much easier to track your progress (and individual changes) that way.
I have started to implement TAGBODY for PARENSCRIPT [A,B,C]. The general idea is to imitate a jump table by looping over a switch-case. A GO (C-terminology: jump) then sets the switch-variable to the next jump destination. The loop subsequently causes the switch to branch to the jump target in the switch-variable. Leaving the tagbody means leaving the loop.
Hmmm, okay. My first thought would've been to use a function for each part and just do tail recursion... but it seems that this isn't really supported in Javascript?!
There are complications. Common Lisp allows nested tagbody-forms. Common Lisp allows go-tags to be referenced within the lexical scope *and* the dynamic extent of a tagbody form. This means that a LAMBDA can close over a go-tag and jump there, see an example in [B], of how inconvenient this can become for compilation to JavaScript.
Yeah... that would be a good reason for simple function calls and tail recursion.
- I need a code review of the algorithm.
The implementation in [B] seems to be satisfactory. There are some test cases and examples. Most there is the most hairy example I could find up to now. I may have missed crucial details.
I'll take a look - but please let's try to get it into the git repo first, so that any discussions have some common state to refer to.
- My understanding of the CL:TAGBODY definition in
the CLHS [4] may be wrong. Which alternate interpretations does anybody here know of?
What are your questions, or points of confusion?
Ad 1: https://gitlab.common-lisp.net/parenscript/parenscript