From: Chad Perrin <perrin@...>
Date: 2006-07-27T04:19:38+09:00
Subject: Re: For performance, write it in C

On Thu, Jul 27, 2006 at 03:55:10AM +0900, Martin Ellis wrote:
> Chad Perrin wrote:
> > Haskell is a better choice than Java for performance: 
> 
> I suspect it depends what you're doing...

To clarify: I meant "on average" or "in general".  Obviously, there will
be instances where Java will outperform Haskell or, for that matter,
even C -- just as there are times Perl can outperform C, for an
equivalent amount of invested programmer time, et cetera.  I suspect the
same is true even of Ruby, despite its comparatively crappy execution
speed.  That doesn't change the fact that in the majority of cases,
Haskell will outperform most other languages.  It is, after all, the C
of functional programming.

> 
> > in fact, the only thing keeping 
> > Haskell from performing as well as C, from what I understand, is the
> > current state of processor design.
> 
> I'm interested to know more about that.
> Could you elaborate?  A reference would do.

I'm having difficulty finding citations for this that actually explain
anything, but the short and sloppy version is as follows:

Because imperative style programming had "won" the programming paradigm
battle back in the antediluvian days of programming, processors have
over time been oriented more and more toward efficient execution of code
written in that style.  When a new processor design and a new
instruction set for a processor is shown to be more efficient in code
execution, it is more efficient because it has been better architected
for the software that will run on it, to better handle the instructions
that will be given to it with alacrity.  Since almost all programs
written today are written in imperative, rather than functional, style,
this means that processors are optimized for execution of imperative
code (or, more specifically, execution of binaries that are compiled
from imperative code).

As a result, functional programming languages operate at a slight
compilation efficiency disadvantage -- a disadvantage that has been
growing for decades.  There are off-hand remarks all over the web about
how functional programming languages supposedly do not compile as
efficiently as imperative programming languages, but these statements
only tell part of the story: the full tale is that functional
programming languages do not compile as efficiently on processors
optimized for imperative-style programming.

We are likely heading into an era where that will be less strictly the
case, however, and functional languages will be able to start catching
up, performance-wise.  Newer programming languages are beginning to get
further from their imperative roots, incorporating more characteristics
of functional-style languages (think of Ruby's convergence on Lisp, for
instance).  For now, however, O'Caml and, even moreso, Haskell suffer at
a disadvantage because their most efficient execution environment isn't
available on our computers.

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
"Real ugliness is not harsh-looking syntax, but having to
build programs out of the wrong concepts." - Paul Graham