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

How to build a successful civilisation i...
GodFinger 2 grants you godlike powers, leaving you to raise a civilization of followers. In the spirit of games like Black & White, the GodFinger games will see you building bigger and better villages, developing more advanced technology and... | Read more »
How to get all the crabs in Mr Crab 2
Mr. Crab 2 may look like a cutesy platformer for kids, but if you're the kind of person who likes to complete a game 100%, you'll soon realise that it's a tougher than a crustacean's shell. [Read more] | Read more »
How to be a star in Britney Spears: Amer...
If you've ever wanted to be a star, baby, then you've probably already checked out Britney Spears: American Dream and are happily making your way up the charts. But fame doesn't come easy, and everyone needs a helping hand sometimes. So we've got... | Read more »
AppSpy is hiring a part time Staff Write...
| Read more »
How to save lives in ER Surgery Simulato...
A serious earthquake has struck a nearby town in ER Surgery Simulator - Emergency Doctor, and it’s up to you to save the victims. [Read more] | Read more »
Tips and tricks to get a high score in G...
Ketchapp Games loves the endless runner genre. And its newest game, Gravity Switch, is no exception. Gravity Switch takes a fresh approach, though, as you move a block, suspended in zero gravity, safely through a maze of shifting pillars. If the... | Read more »
Tips and tricks to get a high score in S...
Smash Fu is a high-paced tile-tapping game that requires quick reflexes and some practice. You’ll have to smash bricks with the skill of a seasoned black belt to get a high score. To raise the stakes a bit, you’ll also have to avoid tapping any... | Read more »
How to keep the ball rolling in Dropple
If you're new to the minimalist puzzler Dropple, you may find yourself struggling to make it beyond the first couple of steps before your ball falls into the endless abyss below. [Read more] | Read more »
Game Craft releases new Legend of War ti...
Set for release at the end of this month, real time strategy title Legend of War seems sure to delight with a veritable feast of sweet features to get stuck into. Developed by Game Craft, the game is due for release through both the App Store and... | Read more »
How not to die in Traffic Rider
Traffic Rider, an Out Run-esque game in which your ride a motorcycle recklessly into trffic, might not seem particularly complicated. [Read more] | Read more »

Price Scanner via MacPrices.net

Apple refurbished iMacs available for up to $...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
Textkraft Professional Becomes A Mobile Produ...
The new update 4.1 of Textkraft Professional for the iPad comes with many new and updated features that will be particularly of interest to self-publishers of e-books. Highlights include import and... Read more
SnipNotes 2.0 – Intelligent note-taking for i...
Indie software developer Felix Lisczyk has announced the release and immediate availability of SnipNotes 2.0, the next major version of his productivity app for iOS devices and Apple Watch.... Read more
Pitch Clock – The Entrepreneur’s Wingman Laun...
Grand Rapids, Michigan based Skunk Tank has announced the release and immediate availability of Pitch Clock – The Entrepreneur’s Wingman 1.1, the company’s new business app available exclusively on... Read more
13-inch 2.9GHz Retina MacBook Pro on sale for...
B&H Photo has the 13″ 2.9GHz Retina MacBook Pro (model #MF841LL/A) on sale for $1599 including free shipping plus NY tax only. Their price is $200 off MSRP. Amazon also has the 13″ 3.9GHz Retina... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
Clearance 12-inch Retina MacBooks available s...
B&H Photo has dropped prices on leftover 2015 12″ Retina MacBooks with models now available starting at $999. Shipping is free, and B&H charges NY tax only: - 12″ 1.1GHz Gray Retina MacBook... Read more
Check Apple prices on any device with the iTr...
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
New 2016 13-inch 256GB MacBook Air on sale fo...
B&H Photo has the new 13″ 1.6GHz/256GB MacBook Air (model MMGG2LL/A) on sale for $1149 including free shipping plus NY sales tax only. Their price is $50 off MSRP. Amazon has the 13″ 1.6GHz/256GB... Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 available starting at $339. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB Wi-Fi iPad Air 2: $499 - 64GB Wi-Fi iPad... Read more

Jobs Board

*Apple* Nissan Service Technicians - Apple A...
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 , Read more
ISCS *Apple* ID Site Support Engineer - APP...
…position, we are looking for an individual who has experience supporting customers with Apple ID issues and enjoys this area of support. This person should be 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
*Apple* Support Technician II - Worldventure...
…global, fast growing member based travel company, is currently sourcing for an Apple Support Technician II to be based in our Plano headquarters. WorldVentures is Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.