foreach ... else statement

[Walter Bright]

Bill Baxter wrote:
> On Thu, Jan 8, 2009 at 6:46 AM, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>> Bill Baxter wrote:
>>> On Thu, Jan 8, 2009 at 5:54 AM, Walter Bright
>>> <newshound1 at digitalmars.com> wrote:
>>>> Sean Kelly wrote:
>>>>>> I keep thinking I should put on a "Compiler Construction" seminar!
>>>>> You should.  The academic courses do a good job with theory and
>>>>> general application, but that isn't quite the same as one based on
>>>>> practical experience.
>>>> That's true. I learned the theory taking a compiler construction course
>>>> at
>>>> Standford, and then tried to apply it. It turns out that there's a lot
>>>> they
>>>> left out <g> that's needed to actually get those optimizations to work.
>>>>
>>>> Loop induction variables was a big one, because the theory never takes
>>>> into
>>>> account the fact that you're replacing a signed loop index with an
>>>> unsigned
>>>> loop pointer. Oops!
>>>>
>>>> It's like in physics class you're always dealing with frictionless brakes
>>>> and pointless masses.
>>> You mean massless points?  Or was that deliberate?
>> I think there were two jokes actually: frictionless brakes (used instead of
>> e.g. frictionless pulleys) which is an oxymoron, and a pun on point masses
>> (objects that can be approximated by a point).
> 
> Hmmm.  Oh yeh.  I'm gonna claim lack of my first morning cup o coffee
> as my excuse for missing that.
> Cute.

School physics problems always start out with "assume there is no 
friction, and the point has no mass."

Academic papers on compiler optimizations always start out with "assume 
there are no pointers, no references, no arrays, no exceptions, no 
threads, no aliasing, no overflows, no signed/unsigned, there are 
infinite registers available, registers are orthogonal, etc." Or they 
just go ahead and let you discover that they assumed that. Useful 
languages are a lot messier in the real world.