Mike Schaeffer's Blog

Not too long ago, I wrote a bit on life with an iPhone 3G. Since then, Apple has revised the platform a few times, and I'verecently upgraded to the iPhone 4S. This makes now as good a time as any to revisit the points in my earlier post to see what has changed:

• Touch Screen - The Apple touch screen is about as good as it gets. The size is a good balance between utility and portability, the hardware is well executed, and the software is very, very fluid. That said, there's still the problem that touch screens eliminate the tactile feedback you get from physical buttons. It's harder to use the phone when your eyes aren't visually focused on the display. This limitation is innate to touch screens, but it's still annoying.

• 'Ambient Information' - iOS 5 handles notifications much more nicely than in earlier versions of iOS. However, the homescreen is still largely dead to ambient information. The only two exceptions are the numeric badges attached to icons and the calendar icon (which displays the current date). The clock icon is wrong, the weather is wrong, and the map is wrong. My hunch is that this is partially to save on battery life, but given that the iPod nano can keep an analog clock icon current, some of this limitation seems gratuitous.

• Inconvenient Portrait/Landscape Switching - Fixed with a nice lock facility in the task switcher. (Although I rarely use the lock, so maybe it wasn't a big problem after all.)

• Multiple e-Mail boxes - Fixed in iOS 4 with the unified mailbox view.

• Large e-mails - I'm not honestly sure if this has been fixed, or if I just get fewer large e-mails, but I haven't noticed this nearly as much.

• Latency - The iPhone 4S is almost completely beyond reproach. (The latency on my old 3G got terrible, with the upgrade to iOS 4.0, and the subseuent patches did nothing to correct it.)

• App Store Rejections - There seems to have been less public drama lately around App Store rejections and policy changes. However, I'm suspecting it's mainly because Apple has given a little and developers have come to grudgingly accept the limitations that Apple still imposes.

• App Store - It's grown to 500,000 (!) applications, but Apple still controls the horizontal and the vertical. Because they control the way applications are displayed, they have a huge degree of control over the exposure their ISV's get and the revenues those ISV's earn.

• Keyboard - After over three years, it's still tedious and error-prone. It works, but just. What's changed in my thinking over the last couple years is that I no longer care. For me, the iPhone is almost entirely about content consumption, and the keyboard doesn't really matter that much.

• Industrial Design - I still love the way the phone looks and feels. What's different for me is that I no longer bother with the add on case.

A couple years ago, this is where I said I wouldn't switch away from an iPhone. I recently replaced one iPhone with another, so for me, this is still mostly true; The iPhone has evolved nicely over the years, and it still fits my needs better than the alternatives. However, two things have changed in the last few years. The first is that there's now a reasonable competitor. Unlike then, the alternative to iOS isn't Windows Mobile 6.5... the modern alternative, Android, has a touch screen, a modern web browser, and a fully stocked app store. Unless Apple sues Android into submission, it has lost these things as competitive differentiators.

The second thing that's changed for me in the last couple years is more personal. As much as I like the iPhone, I can't shake the feeling that it isn't a net improvement to my overall standard of living. Amy Breesman said it well when she was recently quoted in an NPR Story: " I would almost say it's, like, a negative effect that it's had on my life. It's just kind of this rabbit hole that you're always going down.". Maybe I'd miss it more if it were gone, but I can't shake the feeling that the time spent on the phone would be better spent elsewhere. Then again, I wouldn't have known about that NPR quotation, unless I had heard it on the NPR app in my phone.

One typical property of Lisp systems is that they they intern symbols. Roughly speaking, when symbols are interned, two symbols with the same print name will also have the same identity. This design choice has several significant implications elsewhere in the Lisp implementation. It is also one of the places where Clojure differs from Lisp tradition.

In code, the most basic version of the intern algorithm is easy to express:

(define (intern! symbol-name)
   (unless (hash-has? *symbol-table* symbol-name)
      (hash-set! *symbol-table* symbol-name (make-symbol symbol-name)))
   (hash-ref *symbol-table* symbol-name))

This code returns the symbol with the given name in the global symbol table. If there's not already a symbol under that name in the global table, it creates a symbol with that name and stores it in the hash prior to returning it.. This ensures that make-symbol is only called once for each symbol-name, and the symbol stored in *symbol-table* is always the symbol returned for a given name. Any two calls to intern! with the same name are therefore guaranteed to return the exact, same, eq? symbol object. At a vCalc REPL, this looks like so (The fact that both symbols are printed with ##0 implies that they have the same identity.):

user> (intern! "test-symbol")
; ##0 = test-symbol
user> (intern! "test-symbol")
; ##0 = test-symbol

This design has several properties that have historially been useful when implementing a Lisp. First, by sharing the internal representation of symbols with the same print name, interning can reduce memory consumption. A careful programmer can write an implementation of interned symbols that doesn't allocate any memory on the heap unless it sees a new, distinct symbol. Interning also gives a (theoretically) cheaper mechanism for comparing two symbols for equality. Enforcing symbol identity equality for symbol name equality implies that symbol name equality can be reduced to a single machine instruction. In the early days of Lisp, these were very significant advantages. With modern hardware, they are less important. However, the semantics of interned symbols do still differ in important ways.

One example of this is that interned symbols make it easy to provide a global environment 'for free'. To see what I mean by this, here is the vCalc declaration of a symbol:

struct
{
     ...
     lref_t vcell;  // Current Global Variable Binding
     ...
} symbol;

Each symbol carries with it three fields that are specific to each symbol, and are created and initialized at the time the symbol is created. Because vcell for the symbol is created at the same time as the symbol, the global variable named by the symbol is created at the same time as the symbol itself. Accessing the value of that global variable is done through a field stored at an offset relative to the beginning of the symbol. These benefits also accrue to property lists, as they can also be stored in a field of a symbol. This is a cheap implementation strategy for global variables and property lists, but it comes at the cost of imposing a tight coupling between two distinct concepts: symbols and the global environment.

The upside of this coupling is that it encourages the use of global symbol attributes (bindings and properties). During interactive programming at a REPL, global bindings turn out to be useful because they make it easy to 'say the name' of the bindings to the environment. For bindingsthat directly map to symbols, the symbol itself is sufficient to name the binding and use it during debugging. Consider this definition:

(define *current-counter-value* 0)

(define (next-counter-value)
   (incr! *current-counter-value*)
   *current-counter-value*)

This definition of next-counter-value makes it easy to inspect the current counter value. It's stored in a global variable binding, so it can be inspected and modified during debugging using its name: *current-counter-value*. A more modular style of programming would store the current counter value in a binding local to the definition of next-counter-value:

(let ((current-counter-value 0))
  (define (next-counter-value)
    (incr! current-counter-value)
    current-counter-value))

This is 'better' from a stylistic point of view, because it reduces the scope of the binding of current-counter-value entirely to the scope of the next-counter-value function. This eliminates the chance that 'somebody else' will break encapsulation and modify the counter value in a harmful fashion. Unfortunately, 'somebody else' also includes the REPL itself. The 'better' design imposes the cost that it's no longer as easy to inspect or modify the current-counter-value from the REPL. (Doing so requires the ability to inspect or name the local bindings captured in the next-counter-value closure.)

The tight coupling between interned symbols and global variable bindings should not come as a suprise, because interning a symbol necessarily makes the symbol itself global. In a Lisp that interns symbols, the following code fragment creates two distinct local variable bindings, despite the fact that the bindings are named by the same, eq? symbol: local-variable.

(let ((local-variable 0))
   (let ((local-variable 0))
      local-variable))

The mismatch between globally interned symbols and local bindings implies that symbols cannot as directly be involved in talking about local bindings. A Common Lisp type declaration is an S-expression that says something about the variable named by a symbol.

(declare (fixnum el))

In contrast, a Clojure type declaration is a reader expression that attaches metadata to the symbol itself:

^String x

The ^ syntax in Clojure gathers up metadata and then applies it using withMeta to the next expression in the input stream. In the case of a type declaration, the metadata gets applied to the symbol naming the binding. This can be done in one of two ways. The first is to destructively update metadata attached to an interned symbol. If Clojure had done this, then each occurrance of symbol metadata would overwrite whatever metadata was there before, and that one copy of the metadata would apply to every occurance of the symbol in the source text. Every variable with the same name would have to have the same type declarations.

Clojure took the other approach, and avoids the problem by not interning symbols. This allows metadata to be bound to a symbol locally. In the Clojure equivalent of the local-variable example, there are two local variables and each are named by two distinct symbols (but with the same name).

(let [local-variable 0]
   (let [local-variable 0]
      local-variable))

The flexibility of this approch is useful, but it comes at the cost of losing the ability to store values in the symbols themselves. Global symbol property lists in Lisp have to be modeled using some other means. Global variable bindings are not stored in symbols, but rather in Vars. (This is something that compiled Lisps tend to do anyway.) These changes result in symbols in Clojure becoming slightly 'smaller' than in Lisp, and more well aligned with how they are used in moodern, lexically scoped Lisps. Because there are still global variable bindings availble in the language, the naming benefits of globals are still available for use in the REPL. It's taken a while for me to get there, but the overall effect of un-interned symbols on the design of a Lisp seems generally positive.

It took long enough, but finally, I've taken the time to set up a better workflow for this blog:

• The master copy of the blog contents is no longer on the server. It's now on one of my personal machines.
• I'm managing site history using git . This was a nice idea, but git and blosxom have a fundamental difference of opinion on the importance of file datestamps. blosxom relies on datestamps to assign dates to posts and git deliberately updates datestamps to work with build systems. There are ways to reconcile the two, but it's not worth the time right now.
• Uploads to the server are done with rsync invoked through a makefile. (ssh's public key authentication makes this blazingly fast and easy.)

Maybe now, I'll finally get around to writing a little more. (Or, I could investigate incorporating Markdown, or the Baseline CSS Framework, or....)

I've been meaning to write this for months... after switching to an iPhone last October I have some thoughts on the transition away from Windows Mobile. Most of my detailed comments are complaints, so before I continue, it's worth saying that I do think the iPhone is the best smart phone you can buy. It is, by far, the best answer the industry has come up with for this class of device. That said, it's more fun (and potentially useful) to complain:

• Touch Screen - I remember shopping with my parents for a car in the late 80's. One of the cars we looked at was a Buick Riveria with a touch screen in the center console. It was cool, but since it lacked tactile feedback, you had to be looking at it to use it. Flash forward 23 years, and you can replicate this experience in the palm of your hand, for better or for worse.

• 'Ambient Information' - The phone does a poor job of making inforation ambiently available. To see your next appointment, you need to open the Calendar unless the reminder has already displayed. (This could go on the home page.) To be notified of a new e-mail, you need to unlock the phone and look at the home page. (This could be a LED on the case.) As notifications build up, they wind up truncated and incomplete, presumably so they can fit in an artificially small box on the screen.

• Portrait/Landscape - I wake up in the morning and want to check e-mail before I get up.. I grab the phone off the nightstand, look at the display, and it... switches to landscape mode. I'm driving down the road and want to skip a track, so I grab the phone (eyes on the road), put my finger in the general area where the 'forward' button is, and it... switches to landscape mode. Landscape is useful when you need it, and a usability menace when you don't. There needs to be better control over when it engages and when it doesn't. (In this case, physical buttons for skipping forward and backward among tracks might be nice too... Buick ultimately dropped the touch screen entirely, and modern cars with navigation tend to also offer physical controls for key functions.)

• e-Mail - I have two e-mail accounts set up on my phone: personal and business. It takes five taps to switch between them. A unified view would be nice. (A list of the union of all inboxes, color-coded by in-box). An easier way to pick an in-box would be almost as nice.

• Large e-mails - By default, large e-mails are only partially downloaded to the phone and there's a button at the bottom of a one of these mails that lets you download the rest. Of course, once it does, it then zips you back to the top of the mail, so you have to manually scroll through the (remember, it's large) e-mail to get to where you were reading. Argh.

• Latency - Maybe a 3GS would fix this, but the phone seems very slow to change modes and update the display. I find myself continually waiting split-seconds for the thing to animate the transition from one display to the next. I'm asking a lot here, but I don't care... I use the thing most waking hours of most days.

• App Store Rejections - This is a problem, it sucks for app developers, and it won't matter to the success of the platform. The vast majority of customers will never hear that Apple censored a dictionary (!), and even if they did, it won't stop them from buying. In the short term, my guess is that Apple will make whatever minimal changes it needs to make to keep developers quiet enough, and the iPhone will continue to do very well. Phone buyers don't care enough about choice, and App developers will tend to always want to code for the platform where they have the best shot at making money, which is currently the iPhone. In the long term, my guess is that a lot more of this content will wind up on mobile web sites than through the store. After all, a website can be an icon on the home page, avoid the risk of Apple's rejecton, and also get to run on Android, Pre, and Windows Mobile.

• App Store - 25,000 applications on the site, and I might look at 10 or 20 before deciding to make a purchase. The way the store presents applications (controlled by Apple) has a huge impact on which apps succeed and which apps fail. Even if the rejection problem magically goes away, Apple still controls the horizontal and the vertical. (A lot like Google's control over the fate of websites...)

• Keyboard - After ten months, it's still tedious and error-prone for me. It works, but just. Apple should provide a keyboard layout that works like a Blackberry (or even T9) and trades off multiple letters per key in exchange for larger keys.

• Industrial Design - I love the way the phone looks and feels, so I wrap it in a tacky add on case to 'protect it'. So does most everybody else. Last I heard, good design was about making a product that looks good and works well. The rampant sales of cases implies to me that something is missing with the 'works well' part of that equation.

I do like the thing, and I wouldn't switch away, but it's far from perfect. Let's hope it gets better.