The word .S prints out what is on the stack at that time without disturbing it. It will never show you more or less than what is on the stack. If what is on the stack does not make sense it is because of an error in programming and this is very, very easy to do.
One of the most helpful things for me was to write out each line of code (each Word) on a different line and add a comment to the left as to what the stack contents would be afterwards. While this is time consuming it has the benefit of making it clear what is happening to the stack after each step. One of the best parts of Forth is that it encourages you to create small modules which are easier to debug. If you create a new word that is supposed to take two values off the stack and manipulate them and return the result you can check the functionality by clearing the stack, typing in two test values and then executing your new Word. Then to a .S to check the result. Remember though that .S leave the stack contents there so if you want to run another such test you would want to clear the stack first. Jeff Birt From: M100 <[email protected]> On Behalf Of Alex ... Sent: Monday, March 29, 2021 1:25 PM To: [email protected] Subject: Re: [M100] Does anyone actually use MFORTH? Cool, so newbie mistakes and ignorance. As long as my computer's working properly. :) What threw me off is in the book, (pg.25) it talks about returning usually 0 and printing STACK EMPTY, which is definitely not how the machine behaved when trying it. I don't expect everything to have bounds checking, but I'm using .S a lot to inspect the stack, so having to reset the machine all the time and start over kind of sucks. If I knew more about the system maybe I could rewrite .S to know if it's looking at the stack or what's underneath? About the editor: I skipped over the whole chapter on the arcane line editor and page/block-based disk storage since this machine has none of that. Using TEXT with .DO files works ok, as long as whatever I'm doing doesn't trample the files in RAM. Thanks for the tutorial videos, Birt. They've been helpful! If I had a C=64 kicking around here I would definitely give DurexForth a try. On Mon, Mar 29, 2021, 08:37 Jeffrey Birt <[email protected] <mailto:[email protected]> > wrote: This is the default behavior for most all vintage 8-bit Forth implementations. To do a bounds check might take 6-10 machine cycles for every word. This does not seem like a lot, but it would have a noticeable impact on performance. When I ventured Forth a few years ago I found that Forth Inc has a PC based Forth Dev system that is pretty forgiving and a good way to learn without crashing a machine. https://www.forth.com/ . There is also a good online Forth tutorial with a web based Forth implementation: https://skilldrick.github.io/easyforth/ I got the most out of DurexForth which is a modern Forth implementation on the C64. You still get the vintage goodness but with a good VI like editor and actual file support rather than the super goofy and crude typical Forth screens and blocks. I did a few cheesy Forth videos at the time too: https://www.youtube.com/watch?v=TXIDqptXmiM (lots of links in the description). Jeff Birt From: M100 <[email protected] <mailto:[email protected]> > On Behalf Of Alex ... Sent: Sunday, March 28, 2021 9:39 PM To: Model 100 Discussion <[email protected] <mailto:[email protected]> > Subject: [M100] Does anyone actually use MFORTH? Hello Tandy laptop nerds, So I've been reading Leo Brodie's "Starting Forth" and using my '102 as a playground / labrat. There's been a few inconsistencies I expected and can live with/work around, but I've noticed what seems like really bad bugs. It seems trivially easy to underflow the stack into la-la land. (For example: . . .S after a fresh boot will get it stuck spewing memory all over the screen) Has anyone actually used MFORTH for more than just simple tests? Is there maybe some hardware quirks involved here that don't exist on the Virtual-T emulator? Figured I'd cast this one out and see if anyone bites. -Alex -- Disclaimer: Any resemblance between the above views and those of my employer, my terminal, or the view out my window are purely coincidental. Any resemblance between the above and my own views is non-deterministic. The question of the existence of views in the absence of anyone to hold them is left as an exercise for the reader. The question of the existence of the reader is left as an exercise for the second god coefficient. (A discussion of non-orthogonal, non-integral polytheism is beyond the scope of this article.) Thanks /usr/games/fortune
