TweetFollow Us on Twitter

Forth Q and A
Volume Number:1
Issue Number:6
Column Tag:TECH NOTES

FORTH Q&A

By Jörg Langowski

Q: How can I write text and numbers to a window and have automatic wrap- around?

A: For one thing, Forth does not define the simple “.” or type words so as to provide an automatic CR when the end of the window is reached. This makes sense in some applications, such as printing out tables, when the window size is not known beforehand. On the other hand, it is rather annoying if one wants to test a simple definition to see half of the printout disappear off the right edge.

You might have noticed that the built-in Forth word, WORDS, does an automatic word wrap. So it almost looks like there is some hidden word in MacForth that tests for the end of the ‘screen’ and prints out a CR when it is reached. Lets look at the definition of WORDS, using the decompiler from an earlier issue of this journal. (I converted the BRANCHes to IFs etc. to make the code more readable). Please refer to figure 1.

: words
  context @ ?dup 
   if @ ?dup
     if dup @ + ( stack now contains address of latest definition )
        begin dup dup 1+ c@ swap c@ or while ( token <> 0 )
            2+ count 31 and 2dup 16 {2c7c} ( aha! hidden definition )
            dup {2c58} ( another one ) type 2 spaces
            + ( add name length, get next token )
        repeat
     drop then
   then;

Figure 1

The code is pretty sraightforward: The address of the CONTEXT vocabulary is put on the stack and the offset to the LATEST definition added to it. Then, after making sure it is not at the end of the list (token = 0), WORDS gets the name string of the definition and, after some manipulations, types it. The manipulations are done by two of those strange tokens that have no name associated with them, {2C7C} and {2C58}. They are defined as follows:

: {2c7c} col @ over wmod 1+ -
         dup {2c58} col @ if spaces else drop then ;

: {2c58} col @ +
         get.window +wbounds 6+ w@
         get.window +wline.height @ 7-
         w/ > if cr then ;

The first one, {2C7C} tabs to the next integer multiple of n, where n is the number on top of the stack, and wraps around if it would go beyond the limit of the window. The actual wraparound is done by {2C58}, which expects the number of characters to be output on top of the stack. It then compares the final cursor position to (right window edge)/(line height - 7), which is approximately the last column position in the window. If the string would print beyond this last position, a carriage return is output first. The ‘approximately’, by the way, is the reason why WORDS sometimes prints off the screen with non-standard text sizes. The remedy is to increase LINE.HEIGHT.

So you can very easily achieve automatic wrap when outputting text. For string output (with COUNT TYPE) you may redefine:

: wraptype dup 2c58 execute type ;

and any string you output using this word will automatically be confined to the window boundaries (more or less; in case of trouble change LINE.HEIGHT). For number output, you either have to know beforehand how many digits your number will have, or you write your number to string conversion routine and then use WRAPTYPE.

In the near future, we will solve the text output problem (and also the Cut/Paste problem) in a more elegant way by using the TextEdit functions. Stay tuned for an article on that.

Q: How can I get access to the toolbox routines that are not predefined in MacForth?

A: I hope your question has already been answered in one of my recent columns (there is this 3 months’ delay between writing the letter to us and getting the answer), but I’ll repeat that important point here.

MacForth provides defining words that support most of the toolbox routines. They are the following:

OS.TRAP - the address on top of stack (TOS) is an operating system trap, which is compiled into the definition of the following word. On execution, this word takes the 32-bit number on TOS, puts it into register A0 and executes the trap. The result is returned in the variable IO-RESULT.

MT - the address on TOS is a Pascal procedure type trap. All parameters to this procedure are 32-bit items. On execution, the trap is called with all the parameters passed through the stack. They have to be set up in the order given in the trap definition (in Inside Macintosh).

W>MT - the Pascal definition expects one 16-bit item on TOS. Therefore, the (32-bit) item on TOS is converted to a 16-bit item before the trap is called.

2W>MT - same as W>MT, the two topmost items on the stack are converted to 16 bits.

The third type of traps are Pascal function type traps. This means that you have to allocate space, either 16 or 32 bits, by pushing a zero before you push the arguments on the stack. This way, function type traps can be called through MT. For simple functions, MacForth provides four defining words that do this space allocation automatically:

FUNC>W - no argument, 16 bit result (converted to 32 bits)
FUNC>L - no argument, 32 bit result
W>FUNC>L - 16 bit argument, 32 bit result
L>FUNC>L - 32 bit argument, 32 bit result. 

For all other trap calls you have to write your custom stack set-up procedure, which is not too hard. The definition of NEW.CONTROL in the March issue gives an example for that. One important tool in writing such a toolbox trap definition is the routine PUSHW that changes TOS and the stack pointer in such a way that TOS is a 16-bit item:

: pushw s0 @ >r sp@ 2- s0 ! sp! r> s0 ! drop ;

Be cautious in using PUSHW; 16-bit pushes and calls that pull 16 bits have to match, otherwise the stack pointer may be 2 bytes out of frame.

Q: How do I use resources from MacForth?

A: The BLKS files contain no resources (as you might check using a resource editor - some of them are around now - or even a simple disk editor program). If you want to use the resource fork of a file, you have to generate the resources first with Rmaker (this program can also be found on several public domain disks). Rmaker, however, has the annoying habit of deleting the data fork of a file that is presented to him. Therefore, the correct procedure is to create a new file of the correct type and creator with Rmaker and put in the resources that you want. For example, the input to Rmaker might look like:

MyFile
BLKSM4TH

TYPE MENU
   ,1
\14

   ,2
Test
Item1
Item2
(-
Item4
Item5

This will create the file MyFile with the correct type (BLKS) and creator (M4TH) and put the Apple menu (ID=1) and a test menu (ID=2) into the resource fork. Of course, this file does not contain a data fork yet, so you have to add some blocks to it by executing

 “ MyFile” 1 assign
1 open
1 10 append.blocks

and you can put your Forth program text into those blocks. MacForth provides the word OPEN.RSRC for opening the resource fork of a file; you will have to read the resources through the appropriate toolbox routines, since there are no predefined words for getting resources from a file.

Since Forth programs are usually distributed in source form, however, I do not consider resources as critical as in other applications. However, if you develop stand-alone applications in Forth (I have not used Level 3 yet, but any comments are welcome), you might want to add the resources with Rmaker. I will deal with using resources in one of my next columns.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to become the ultimate robot warrior...
Chrono Strike is a delightfully immersive beat ‘em up with a sense of humor (any game with a good Sims reference gets points in my book). [Read more] | Read more »
Tips and tricks to get a higher score in...
Snow Roll is a devilish endless runner very much in the vein of Flappy Bird. It revels in its dastardly level of difficulty, and doesn’t really care how angry you get at it as it knows you’ll keep coming back for more. [Read more] | Read more »
How to win big in Slots Deluxe
Cheating while gambling is illegal and morally wrong, and in some parts of the world it leads to men with names like Vinnie "Six Knuckles" Manchenzo beating you to a pulp in a dark alley. [Read more] | Read more »
How to take over the world in Dictator 2
Running a country isn't easy - especially when you're a dictator who wants to take over the world and crush everyone in your path while you do it. [Read more] | Read more »
Tips and tricks to get a higher score in...
Tank.iois - you guessed it! - another multiplayer arena battler likeAgar.io and Slither.io. It does differentiate itself by putting you in a tiny tank though, so it's not exactly the same. To help you get that all-important high score, we've got a... | Read more »
How to unlock characters in One Tap Tenn...
As the title suggests, One Tap Tennis requires only a single tap to play its particular brand of tennis, and rewards you with a ton of unlockable characters if you perform well. Fortunately for you, we at 148Apps have got a few tips and tricks to... | Read more »
Grab it now: Game Craft’s Legend of War...
The real time strategy game is now available for you to sink your teeth into, through the App Store and Google Play. Combining elements of skill, strategy and empire building, Legend of War is a real gamers’ game. [Read more] | Read more »
Skateboard Party 3 ft. Greg Lutzka (Gam...
Skateboard Party 3 ft. Greg Lutzka 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Skateboard Party is back! This third edition of the popular sports franchise features professional skater... | Read more »
Cubious (Games)
Cubious 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Cubious – How smart are you? How high is your IQube? Solve the impossible puzzles to find out, and help a lost little cube find his... | Read more »
Goat Simulator Waste of Space (Games)
Goat Simulator Waste of Space 1.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.1 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** | Read more »

Price Scanner via MacPrices.net

Enterprise Workers Pick Technology Over Perks...
New Adobe study shows surprising attitudes about office jobs and where the future of work is heading. Adobe has released survey findings revealing that a surprising 70 percent of U.S. office workers... Read more
Memorial Day Weekend Sale: $50-$100 off 11-in...
B&H Photo has 13″ and 11″ MacBook Airs with 256GB SSDs on sale for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/256GB MacBook Air: $999 $100 off MSRP... Read more
Memorial Day Weekend Sales: Apple MacBook Pro...
B&H Photo has 13″ and 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz... Read more
Memorial Day Weekend Sales: Apple iMacs and M...
Take up to $150 off the price of a new iMac or Mac mini at the following Apple resellers this Memorial Day weekend: iMacs: B&H Photo has 21″ and 27″ iMacs on sale for up to $150 off MSRP... Read more
Apple refurbished Retina MacBook Pros availab...
Apple has Certified Refurbished 2015 13″ and 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Goal Zero and OtterBox Partner to Expand iPh...
Goal Zero, specialists in portable power, have announced a partnership with OtterBox, brand smartphone case protection, to offer the Slide and Slide Plus Batteries as modules compatible with the new... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Clearance 2015 13-inch MacBook Airs available...
B&H Photo has clearance 2015 13″ MacBook Airs available for $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more

Jobs Board

*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Project Engineer - Smart Source Inc...
SmartSource is in need of an Apple Project Engineer for a 12 month contract opportunity in Pittsburg, PA. Role: Apple Project Engineer Location: Pittsburg, PA Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
Service Assistant - *Apple* Chevrolet *App...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
Editor, *Apple* News - APPLE (United States...
Job Summary The Apple News team is looking for a passionate and knowledgeable editor with experience covering entertainment/pop culture and experience running social Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.