foreach ... else statement

[Andrei Alexandrescu]

Walter Bright wrote:
> 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.

Well that should be taken with the traditional grain of salt.

Andrei