Thursday, June 26, 2008

Blogging from Emacs

As a brief diversion from the Factor stuff I've been working on, I wanted to just share a bit of information that someone out there may find useful.

g-util.el and various frustrations

Since I first saw it, I wanted to use the gblogger-* functions for emacs that g-util.el gives. However, I ended up having a bunch of problems that I was unable to fix and soon gave up. However, yesterday I decided to have another go at it and managed to get it working! It turned out to only require two changes, but they didn't seem to be well-documented anywhere...So, without further ado, here's how to get the g-util stuff working in emacs (your mileage may vary, of course):

  1. Make sure the shell is set to bash. I initially had the shell set to zsh, which resulted in parsing errors
  2. It seems that w3m-buffer doesn't work as the g-html-handler. I set it to switch-to-buffer, which seems to work
And that's it! Enjoy blogging via Emacs!

Monday, June 23, 2008

Factor and Emacs!

As previously mentioned, I've been working on an implementation of Lisp in Factor. Although it's been tough, progress is being made. However, I'm taking a short break from that to work on something just as fun - writing a (better) factor-mode for emacs.

While Factor does come with a factor mode (in factor.el), it has some warts that I don't really like. For one, it doesn't support customization (via customize-group). I'm also not too fond of it's font-lock (that is, syntax highlighting) support, so I'm working on fixing that too. Once I get that working, I'm also going to add some factor-specific movement functions, and prehaps the ability to look up definitions of words and the like. I'd really like to have eldoc-like display of the stack effect of the factor word at point. That would probably entail having a nice inferior-factor mode too, which should be entertaining.

That's it for now!

So yeah, just a quick summary of what I'm up to now. Emacs is just so much fun, not only to write code in, but to write code for! Next time I write, I'll hopefully have made more progress on both factor-mode and extra/lisp.

Monday, June 16, 2008

Factor and Lisp, part three

Since last time I wrote about the state of my lisp-in-factor implementation, not much actual forward progress has been made. Instead, I was embroiled in a struggle to figure out how I was to properly implement the passing of arguments to lisp functions, specifically in the case of function calls.

The problem:

First, some background on my lisp converter: It essentially works by converting lisp forms to factor quotations in the following manner: (foo bar baz) ⇒ [ bar baz ] T{ lisp-symbol f "foo" } funcall (By the way, the T{ ... } is a literal tuple, which you may know as an object. So, T{ lisp-symbol f "foo" } is the literal (i.e. you could type that directly into a Factor listener and it would recognize it as a lisp-symbol object) for a lisp-symbol object whose delegate is f (which they usually are, since delegates are deprecated) and whose name field is "foo") In other words, we get a quotation containing the arguments to the function, which funcall will look up and then call appropriately. Certain primitive forms (e.g. quote, lambda, etc) are built-in primitives that are translated at parse time, but everything else will follow this general form.

Okay, that works...but what if we have something like this? (list 1 2 (list 3 (list 4) 5)) Hm...well, if we translate it the same why we did above, it ends up looking like this: [ 1 2 [ 3 [ 4 ] T{ lisp-symbol f "list" } funcall ] T{ lisp-symbol f "list" } funcall 5 ] T{ lisp-symbol f "list" } funcall Now, this is a problem...the argument list for that outer list is a literal quotation, which includes inner quotations, lisp-symbols and funcall words. This means that the arguments to list, rather than numbers and other lists (which is clearly what is intended here) will be quotations, symbols, and words...which is not what we want at all.

So, how to fix this? Well...I tried a few, fairly hackish methods, such as doing a pretty hideous reduce over the quotation inside funcall, to find occurences of the funcall word, then execute funcall on the last two elements of the quotation...blah, gross. I had been thinking...what I basically want to do is call the argument-list quotation, but somehow keep the result of calling it in a quotation. I toyed with the idea of making everything in the argument list into quotations, then doing a [ call ] map over the argument list (that is, evaluate each element of the quotation, putting the result into another list). However, doing this would require some fairly significant refactoring, and would make the rest of the code much less elegant, as the argument list shown above, rather than [ bar baz ], it would have to be [ [ bar ] [ baz ] ], or, even worse, [ [ 1 ] [ 2 ] [ [ 3 ] [ [ 4 ] [ ... ] ] ] ] get the idea. Very gross. However, while on #concatenative the other day, I asked slava about the possibility of writing a word that word that would take a quotation, call it, then put everything that calling the word put on the stack into a quotation...

Will that work?

It turns out that a superior version of the word I was looking for already exists: with-datastack. This word takes an array, which acts as the stack, a quotation, which it calls, and returns the array/stack, which now has the results of calling the quotation. For example: { 1 2 3 } [ + ] with-datastack . would output { 1 5 }. This can now be used to easily rectify my problems! In funcall, before looking up the variable name and calling the resultant quotation, it does 1array [ call ] with-datastack >quotation to the quotation which contains the argument list. Simple, easy, and clear!

What next?

Although I've said it before, it looks like I'm nearly done the factor side of this...All I have left to do is fix up my implementation of macros and provide facilites for loading and interpreting/compiling lisp files and I'll be just about done! At that point, I'll start bootstraping the lisp implementation in lisp itself, but the real "hard work" will be done. Wish me luck!

Tuesday, June 03, 2008

Factor and Lisp, part two

I've been continuing my work on extra/lisp, and I've finally realized the solution to my current problem, that of macros. The solution, in a nutshell, was to replace the arrays I'd been using to represent lisp s-expressions with actual linked lists. After Slava pointed this out to me, I began work on a simple implementation of the lists. However, my work had not gone far, when the good doublec suggested that, as there was a great deal of overlap, I move my extra/lisp/conses to extra/lists and merge it with extra/lazy-lists (now known as extra/lists/lazy). This took a while, as I also ended up refactoring lazy-lists to use new style accessors and then had to go through all the vocabs that used lazy-lists (which actually wasn't that many) to figure out which needed to be USING: lists, lists.lazy or both.

And then, things get interesting!

After this, things began to get odd...A test starting failing in extra/lists/lazy. It seemed that >>nil? (which, if you're not familiar with factor is a "new-style" accessor: You'd use it like obj new-nil?-val >>nil?, and would leave the modified obj on the stack - elegant, n'es pas? (the converse of that would be nil?>>, which would work like obj nil?>>, and would leave obj's value of nil? on the stack)) was being called on the wrong type of object: That accessor is supposed to be called on a memoized-cons, but was being called on a lazy-filter. This seemed patently impossible to me, as the only place that the word was called was in a method of memoized-cons, meaning that the only possible value that could be on the stack was a memoized-cons.

n After puzzling this one over for a while, and vainly trying to use Factor's normally very usefully walker to determine what was happening, I brought the matter to the attention of the gurus of #concatenative. At the recommendation of doublec, I tried inserting print statements in the word, to figure out where the object was changing from a memoized-cons to a lazy-filter.

The results left me even more puzzled than before.

My descent into madness intensifies

Initially, I tried just printing out the object that >>nil? was dispatching on: As expected, I saw that, while the first dozen times it was called, it was receiving the proper memoized-cons object, it was indeed ending up with a lazy-filter. Okay...that shouldn't be happening, but I already know that it is, so that's at least somewhat expected. What happened next was, however, quite unexpected.

"Well," I thought. "I can see that it's a lazy-filter here...but it must be a memoized-cons when it enters...I know, I'll put print statements throughout the word, so I can see just where it changes!"

Now, below is the word sans debugging print statements:

M: memoized-cons nil? ( memoized-cons -- bool )
    dup nil?>> not-memoized? [
        dup original>> nil? [ >>nil? drop ] keep
    ] [
    ] if ;

(if you don't understand this, go to the Factor home page, and start learning)

After adding various debugging print statements, it looked like this:

M: memoized-cons nil? ( memoized-cons -- bool )
    "Entering nil?: " write dup class . dup nil?>> not-memoized? [
        "True branch: " write dup class . dup original>> nil? [ "Now at >>nil?" write over class . >>nil? drop ] keep
    ] [
        "False branch: " write dup class . nil?>>
    ] if "\n" write;

So now, after reloading lists.lazy and running the test case, I get a bunch of output like this:

Entering nil?: memoized-cons
True branch: memoized-cons
Now at >>nil?: memoized-cons

Entering nil?: memoized-cons
False branch: memoized-cons

Entering nil?: memoized-cons
True branch: memoized-cons
Now at >>nil?: memoized-cons
So, ready for the weird stuff? Here're the last two calls...
Entering nil?: memoized-cons
False branch: memoized-cons

Now at >>nil?: lazy-filter
Um...what? The print statements at the begining of the word, and on the conditional branch that was taken aren't being called. It seems that it's somehow jumping into the middle of the word, without calling anything prior to this one section.

What Next?

Well, I have no idea why this happening. doublec hypothesizes that I've exposed a bug in method dispatch. I'm not sure what else I can do, if that is indeed the case...I guess I'll wait until Slava returns and see if he can figure it out.

In the meantime, I guess I'll keep working on extra/lisp, which was the point of this whole exercise, was it not?

Update:The next day, I went through the code some more and realized I was looking at the wrong place: The bug was actually in the code for lazy-filters, and had to do with the transititon to new-style accessors. The skip word needed a drop at the end, since the new >>foo has the stack effect ( obj newval -- obj ), while the old version it replaced, set-obj-fo had the effect ( newval obj -- ).