TweetFollow Us on Twitter

Winter 91 - THE VETERAN NEOPHYTE

THE VETERAN NEOPHYTE

LISP, COLOR ICONS, AND LAYERS

DAVE JOHNSON

I recently started learning Lisp, in order to write a color icon editor for a project in ACOTSM (that's Apple Classroom of Tomorrow). The people behind ACOT are creating an environment in which kids can build and explore simulated ecologies, and I wanted to help, but didn't know Lisp well enough to be of much use. A color icon editor was needed, and it seemed like a straightforward and painless little project to cut my Lisp teeth on. Hah.

I did learn lots of Lisp, but I spent a disproportionate amount of time learning the low-level system interface in Macintosh Allegro Common Lisp (MCL) and wrestling Color QuickDraw to the ground. For you CopyBits fans, did you know that CopyBits always assumes that the destination PixMap is on the current GDevice? I guess I already knew this--it's documented all over the place--but the implications never affected me before. I needed to convert a 4-bit PixMap to 8 bits, so hey, let's use CopyBits, right? Wrong. The colors got munged every time, because color mapping kicked in and the source's color table didn't match the GDevice's. For the gory details, see Technical Note #277, especially the section on color mapping. If you like CopyBits, you'lllove this tech note.

I was curious what others thought of Lisp, so I asked around a little. Here are some of the responses I got:

Functional languages are cool if you have good libraries, but all those parentheses are a pain in the ass.
-- Bryan "Beaker" Ressler, C programmer.

It's the shortest distance between conception and realization.
-- Matthew MacLaurin, self-admitted Lisp junkie.

I hate it.
-- Neil Day, who was forced to write the Tower of Hanoi iteratively in an introductory Lisp course.

It's a great productivity tool, and Common Lisp provides a rich (though perhaps Byzantine) programming environment.
--Gregg Williams, technical writer and sometime Lisper.

(expectant look)
-- Natty, my dog.

There are several immediately apparent things about Lisp that are foreign to people used to C or Pascal. Data typing is nonexistent unless you want it: Any variable can hold any type of data at any time. Functions can be data, too, and can be passed around all over the place. Everything is cozily wrapped in parentheses many levels deep (after a while, this is somehow comforting). Context is all important and omnipresent. Changes can be immediately tried out, so forprototyping (and for those of us who thrive on immediate gratification) it's a joy to work in. For those lacking in discipline, Lisp can help to create a real mess (of course, any language can do that for you, it's just easier in Lisp). Because it is so forgiving, it encourages my own built-in "middle-out" design

strategy, which in the long run isn't terribly efficient, although lots of fun. With a little self-control, of course, this problem would go away (left as an exercise for the reader).

Writing Lisp code that is QuickDraw intensive is kind of a pain at first. MCL provides great libraries for basic QuickDraw tasks, but if you want to get fancy, you have to do it yourself. For the icon editor, I needed lots of little utility routines to do stuff like find a particular color's pixel value in the color table, add a color to a color table, copy a cicn, change the depth of a cicn, build new cicns from scratch. Nearly half my code consists of these little utilities. They'd be needed regardless of the language, I guess, but writing them in Lisp required me to learn the low-level system interface much more thoroughly than I originally intended. This made me grumble a little, but after I'd gotten over the initial syntactical hump, low-level access became transparent and largely effortless.

The other half of the code was much Lispier. I used the built-in object system (Object Lisp, since I was using MCL 1.3.2. Now, in MCL version 2.0, it's the Common Lisp Object System, or CLOS), and I found that it successfully isolated me from most of the grungy system details like events and window handling (that's what it's supposed to do, right?). I haven't done a lot of object programming, so I can't make incisive comparisons with other object systems, but I liked it.

The sort of layered, threaded structure of Lisp, and the continual "level switching" I had to do during development, got me thinking about how the machine is getting progressively more distant from the software I write. It seems that I write software to live on top of other software, not software to live on a machine. Object programming is a kind of layer creation, in that a well- designed object hides lots of details from the user of the object. MacApp is a layer (a thick one), HyperCard is also a layer (a really thick one), the Mac ® Toolbox is a layer, and so on.

More and more, programmers need to be comfortable stuffed between these layers. Here's the hard truth: YOU NO LONGER HAVE TOTAL CONTROL OF THE MACHINE. Once upon a time, in the dim and distant past, programmers had absolute power over every aspect of the computer. There wasn't even any such thing as a user! A programmer was God in a monotheistic universe. Now there are all sorts of software smoke screens between your code and the machine itself. You are no longer God; at best, you are a minor demigod in charge of shoes, or something. A long time ago I read a discussion of Macintosh programming, and one person compared it to sitting in a dark closet by yourself, and occasionally answering a note that is passed under the door from the outside. I think that's exaggerating a little, but the point is valid. You no longer need to know everything that's going on in the house; you can just be responsible for your own room. At least, that's the idea . . .

One persistent problem is that you have to depend on the reliability of the other code. When my icon editor was almost done, I found a memory leak. Two tiny handles were left on the heap after closing the editor. It took me almost a week (and some expert help) to track it down to a bug in the MCL object system. Obviously, this diluted the benefits gained by using the system.

Overall, though, I really do think that this division of labor, this layering, is a good thing. It lets people find the niche they like best, and ignore much of the rest if they want to. Often it is an incredible time-saver to learn to use others' code rather than learning to do what they did from scratch. Ideally, the layers will insulate you completely from irrelevant detail, and allow you to focus on your task. We're not there yet, but someday, maybe, you can actually stop inventing the wheel.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

MacFamilyTree 7.3.3 - Create and explore...
MacFamilyTree gives genealogy a facelift: it's modern, interactive, incredibly fast, and easy to use. We're convinced that generations of chroniclers would have loved to trade in their genealogy... Read more
Skype 7.5.0.738 - Voice-over-internet ph...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
PushPal 3.0 - Mirror Android notificatio...
PushPal is a client for Pushbullet, which automatically shows you all of your phone's notifications right on your computer. This means you can see who's calling or read text messages even if your... Read more
Logic Pro X 10.1.1 - Music creation and...
Apple Logic Pro X is the most advanced version of Logic ever. Sophisticated new tools for professional songwriting, editing, and mixing are built around a modern interface that's designed to get... Read more
VLC Media Player 2.2.0 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Sound Studio 4.7.8 - Robust audio record...
Sound Studio lets you easily record and professionally edit audio on your Mac. Easily rip vinyls and digitize cassette tapes, or record lectures and voice memos. Prepare for live shows with live... Read more
LibreOffice 4.4.1.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
VueScan 9.5.03 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Freeway Pro 7.0.3 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
Cloud 3.3.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more

This Week at 148Apps: February 23-27, 20...
Final February Fun at 148Apps   How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you’re looking for. The ones we love become Editor’s Choice, standing out... | Read more »
GDC 2015 – Does Not Commute is Definitel...
GDC 2015 – Does Not Commute is Definitely a Game You Should Keep an Eye on Posted by Rob Rich on March 2nd, 2015 [ permalink ] We were teased about Mediocre Games’ (Smash Hit, | Read more »
F84 Games & POW! Announce Stan Lee V...
F84 Games has announced that it is working with legendary comic creator Stan Lee and POW! Entertainment to produce Stan Lee’s Hero Command. The game will be a action adventure of heroic proportions. | Read more »
Setlyst Keeps Your Set Straight So You C...
Setlyst Keeps Your Set Straight So You Can Focus On Rocking Out. Posted by Jessica Fisher on March 2nd, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Space is Vast, So Space Agency Has a Vas...
Space is Vast, So Space Agency Has a Vast New Update! Posted by Jessica Fisher on March 2nd, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Size DOES Matter Review
Size DOES Matter Review By Campbell Bird on March 2nd, 2015 Our Rating: :: HARD TO BEATUniversal App - Designed for iPhone and iPad This rhythm game has a unique control scheme and performance system that make it feel like a true... | Read more »
The first ever action 3D card battler Al...
On the other hand, you probably haven’t played an action 3D card battler – until now. Step forward, All Star Legion. All Star Legion is a 3D QTE-based action RPG card battler, but fear not – the game itself isn’t as convoluted as its description.... | Read more »
Travel Back to the 1980s With the Making...
Headup Games has released a hilarious making of video for its upcoming title, Pixel Heroes: Byte & Magic. The game is a RPG/Roguelike where you control three heroes set to save the township of Pixton from an evil cult called The Sons of Dawn.... | Read more »
Heavenstrike Rivals Review
Heavenstrike Rivals Review By Campbell Bird on March 2nd, 2015 Our Rating: :: HEAVENLY STRATEGICUniversal App - Designed for iPhone and iPad Despite a few flaws, this free-to-play strategy game is a fun mix of new and old strategy... | Read more »
Get The Whole Story – Lone Wolf Complete...
Get The Whole Story – Lone Wolf Complete is Now Available and On Sale Posted by Jessica Fisher on February 27th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »

Price Scanner via MacPrices.net

Sale! 15-inch 2.2GHz Retina MacBook Pro for $...
 Best Buy has the 15″ 2.2GHz Retina MacBook Pro on sale for $1774.99 $1799.99, or $225 off MSRP. Choose free home shipping or free local store pickup (if available). Price valid for online orders... Read more
27-inch 3.5GHz 5K iMac in stock today and on...
 B&H Photo has the 27″ 3.5GHz 5K iMac in stock today and on sale for $2299 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price available for... Read more
Apple Launches Free Web-Based Pages and Other...
Apple’s new Web-only access to iWork productivity apps is a free level of iCloud service available to anyone, including people who don’t own or use Apple devices. The service includes access to Apple... Read more
Survey Reveals Solid State Disk (SSD) Technol...
In a recent SSD technology use survey, Kroll Ontrack, a firm specializing in data recovery, found that while nearly 90 percent of respondents leverage the performance and reliability benefits of SSD... Read more
Save up to $600 with Apple refurbished Mac Pr...
The Apple Store is offering Apple Certified Refurbished Mac Pros for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
Apple CEO Tim Cook to Deliver 2015 George Was...
Apple CEO Tim Cook will deliver the George Washington University’s Commencement address to GWU grads on May 17, at which time he will also be awarded an honorary doctorate of public service from the... Read more
Apple restocks refurbished Mac minis for up t...
The Apple Store has restocked Apple Certified Refurbished 2014 Mac minis, with models available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz... Read more
Save up to $50 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549 $50 off - 128GB iPad Air 2... Read more
16GB iPad Air 2 on sale for $447, save $52
Walmart has the 16GB iPad Air 2 WiFi on sale for $446.99 on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale price for online orders only,... Read more

Jobs Board

*Apple* Pay Automation Engineer - iOS System...
**Job Summary** At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring passion and dedication to your job Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.