[Haskell-cafe] Strange type behavior in GHCi 6.4.2

Bulat Ziganshin bulat.ziganshin at gmail.com
Mon Jan 1 05:55:56 EST 2007

Hello Lennart,

Sunday, December 31, 2006, 10:26:24 PM, you wrote:

> I think you can be much more productive in optimizing your code
> if you actually understand what's going on.  I usually don't go as
> far as looking at compiler intermediate code; I usually stick with
> profiling (or look at assembly code if it's a really performance
> critical inner loop).

for GHC??? :)  if we say about optimizing C programs, old days i usually
looked into asm code and then darken and go to rewrote it in asm :)
nowadays i look only at memory access patterns, it's enough, at least for a
few programs i optimized this year

for GHC, i usually know which functions need to become faster, so i
personally don't need profiling. moreover, program should be optimized for
wide variety of situations, while profiling run shows only one execution

i don't think that looking into STG (don't even said about C--/asm) may
help me to optimize program. which program-specific things i can find here,
after i've once learned how generation of STG code works?

> Then you can start optimizing.  That can be
> by changing algorithm, changing data representation, strictness
> annotations, etc.

yes, i don't use profiling because i use more specific instruments to
investigate performance bottlenecks

> It can also be by inserting some INLINE or SPECIALIZE
> pragmas, but that's more rare (don't get me wrong about those pragmas,
> I introduced them in Haskell with hbc).  But I think just adding pragmas
> willy-nilly is a bad idea; I find that most serious performance problems
> cannot be solved by those means, instead you need a higher level  
> approach.

i proposed it as fast approach to raise performance, as alternative to your
suggestion to profile and read code, where you not said anything about
changing algorithms :)

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com

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