[M3commit] CVS Update: cm3

[Tony Hosking]

That is you view, but at odds with why Modula-3 was designed the way it was.  I think we've already had this conversation before.  The point is that even when a variable is initialised to 0 as you prefer there may still be bugs in the program.

You are seeing Modula-3 through C spectacles, where so much of the language is undefined.

On 5 Jul 2010, at 17:51, Jay K wrote:

> 
> As a human reading code (very finite cycles), I don't like to see:
> 
> 
> VAR a: type;
> BEGIN
> ...
> END
> 
> 
> no matter the contents of "...".
> 
> 
> I'd much rather see:
> 
> 
> VAR a: type := 0;
> 
> 
> 
> and know very quickly and without a doubt that a is never used uninitialized.
> I've been bitten too much by microoptimizations around not initializing locals.
> Some large fraction of the time the compiler will optimize away the initialization.
>   (ie. depending on the contents of "...")
> Some other large fraction of the time the performance difference will be unmeasurable.
>    So much code is I/O bound already, let alone compute bound by more significant "algorithmic" factors.
> And then some small fraction of the time, maybe, it will be a bad pessimization.
> 
> 
> I just don't think it is worth the risk.
> 
> 
>  - Jay
> 
> 
> 
> ----------------------------------------
>> Subject: Re: [M3commit] CVS Update: cm3
>> From: hosking at cs.purdue.edu
>> Date: Mon, 5 Jul 2010 17:34:51 -0400
>> CC: m3commit at elegosoft.com
>> To: jay.krell at cornell.edu
>> 
>> Huh?
>> 
>> On 5 Jul 2010, at 17:15, Jay K wrote:
>> 
>>> 
>>> At least some of these were Word.T. "valid" is still "random" and the code is unpredictable, at least by a quick read, even if type safe.
>>> Type safe is just a minimum bar, one that should always be exceeded, even if the compiler is completely unable to validate it.
>>> 
>>> That is, the compiler guarantees are from sufficient relative to correctness.
>>> 
>>> - Jay
>>> 
>>> ----------------------------------------
>>>> From: hosking at cs.purdue.edu
>>>> Date: Mon, 5 Jul 2010 16:50:00 -0400
>>>> To: jay.krell at cornell.edu
>>>> CC: m3commit at elegosoft.com
>>>> Subject: Re: [M3commit] CVS Update: cm3
>>>> 
>>>> But we've been this route before. Modula-3 ensures every variable is initialised with a valid value. I don't see how your adding an initialiser makes it more obviously correct.
>>>> 
>>>> On 5 Jul 2010, at 16:45, Jay K wrote:
>>>> 
>>>>> 
>>>>> I will maybe see about doing better here.
>>>>> Initializing locals doesn't seem like such a bad change though.
>>>>> I like the code to be "obviously correct" by a quick read by a human.
>>>>> 
>>>>> - Jay
>>>>> 
>>>>> ----------------------------------------
>>>>>> From: hosking at cs.purdue.edu
>>>>>> Date: Mon, 5 Jul 2010 14:31:01 -0400
>>>>>> To: jkrell at elego.de
>>>>>> CC: m3commit at elegosoft.com
>>>>>> Subject: Re: [M3commit] CVS Update: cm3
>>>>>> 
>>>>>> Jay, I am perplexed that we are adding things to Modula-3 source because of compiler backend brokenness just to avoid back-end warnings. Better to fix the backend so that RAISE is noreturn. This should not be difficult to do.
>>>>>> 
>>>>>> On 5 Jul 2010, at 15:22, Jay Krell wrote:
>>>>>> 
>>>>>>> CVSROOT: /usr/cvs
>>>>>>> Changes by: jkrell at birch. 10/07/05 15:22:28
>>>>>>> 
>>>>>>> Modified files:
>>>>>>> cm3/m3-tools/cvsup/suplib/src/text_cm3/: SupMiscText.m3
>>>>>>> 
>>>>>>> Log message:
>>>>>>> ../src/text_cm3/SupMiscText.m3: In function 'SupMisc__DecodeWS':
>>>>>>> ../src/text_cm3/SupMiscText.m3:211: warning: 'M3_Bkn9rd_ch' may be used uninitialized in this function
>>>>>>> ../src/text_cm3/SupMiscText.m3:211: note: 'M3_Bkn9rd_ch' was declared here
>>>>>>> 
>>>>>>> because raising an exception isn't currently "noreturn"
>>>>>>> so initialize it to 0
>>>>>> 
>>>>> 
>>>> 
>>> 
>> 
>