[Haskell-cafe] Can Haskell outperform C++?

Kevin Charter kcharter at gmail.com
Wed May 16 19:44:31 CEST 2012

On Wed, May 16, 2012 at 8:40 AM, Gregg Lebovitz <glebovitz at gmail.com> wrote:

> 1) Does Haskell and its libraries need performance improvements?  Probably
> yes. Some of the performance issues seem to be related to the way the
> language is implemented and others by how it is defined. Developers really
> do run into performance issues with Haskell and either learn to work around
> the issue or try to fix the offending implementation. The wiki performance
> page gives insight into some of the performance issues and how address them.

I think there is a closely-related issue: that you'll need to learn how to
debug subtle performance problems *early* in your Haskell programming
career. In particular

   - you will have space leaks and related performance problems in
   naively-written programs
   - you will consequently need to learn how to use strictness annotations
   and other related language features, and how to use the profiler to
   determine where they're needed

For example, imagine you're new to the language, and as an exercise decide
to write a program that counts the characters on standard input and writes
the count to standard output. A naive program in, say, Python will probably
use constant space and be fairly fast. A naive program in Haskell stands a
good chance of having a space leak, building a long chain of thunks that
isn't forced until it needs to write the final answer.  On small inputs,
you won't notice. The nasty surprise comes when your co-worker says "cool,
let's run it on this 100 MB log file!" and your program dies a horrible
death. If your friend is a sceptic, she'll arch an eyebrow and secretly
think your program -- and Haskell -- are a bit lame.

The example is contrived, but it's a very common task to consume some big
stream of input and produce a much smaller summary of it. I think it's fair
to say that you have to be a slightly sophisticated Haskell programmer to
do those kinds of things correctly, at least compared to more mainstream

My experience is that this is perhaps the most important  'problem' with
Haskell performance. Not so much that it's typically two or three or ten
times slower than language X, but that it's easy to have a bad
experience *early
on*, one that seems inconsistent with the language shoot-out and other
performance comparisons.

Kevin Charter
kevin.charter at acm.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20120516/18c1b4f4/attachment.htm>

More information about the Haskell-Cafe mailing list