[erlang-questions] At what point am I "playing compiler"

John Haugeland <>
Sun May 24 23:10:12 CEST 2009

>> I wonder why you believe this. ...
>> Do you have any data to back up this claim, that premature
>> optimization is more common than inadequate forward design?
> Data? Only my noticing that programmers prefer the seductions and small

In other words, "no".  You have made an argument based on an
expectation presented as fact.

> payoffs of design. But ymmv.

Actually, the mileage of every programmer in every team I've run for
whom I still have PSP/TSP data varies, without exception, a record
going back over nearly 60 people and 12 years (almost 100 solid
man-years).  That's the problem with expectation driven argument: it's
rarely if ever correct, no matter the experience level or
sophistication of the arguer.

>>> If it's needed, it's needed. If it's not, it's not. That is a rule of
>>> thumb
>>> that is essentially Knuth's rephrased.
>> We disagree on this point.  I would recommend a reading of the text;
> Few would disagree that if it's not *needed* it should not be done, since

Do you have any data to back up this new assertion, or is this more
expectation presented as fact?

Incidentally, this is argumentum ad populam; it's trivially easy to
display large groups of professionals making bad decisions because of
what few would disagree about.

For what it's worth, I would argue this openly, and my PSP/TSP data
shows clear trends suggesting that designs made with an eye for
performance are both more likely to be completed on time and in fact
more likely to be completed at all.  I cannot imagine making this many
decisions in my professional life based on guesswork, without ever
having measured the results of the things I would soapbox to others,
to find out whether indeed I was correct.

It is indeed not particularly surprising that fully planned work
suffers fewer crippling irreconcilable defects than other work, to
those who've taken the time to actually measure data instead of

There were many people who were very certain that leeches cured the
Bubonic Plague, too.  Including basically the entire European medical
establishment of the germane several multiple-year passes the disease
took through its two hundred year cycle through the continent.
Indeed, they also believed in something called fundamental exhaustion,
where there was just so much willpower God put into a body, and if
exertion was not *needed* it should not be done, because just like
your yellow humors, black humors and sperm, when you used it up it was
gone forever.

Please have numbers to back up your next assertion, Hippocrates.

> optimisation usually brings other costs.

Yeah.  Other costs you imagine.  Got any data to back up those costs?
(Hint: the plural of anecdote is not data.)

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