[Haskell-cafe] Need help - my haskell code is over 50 times slower than equivalent perl implementation

[Nicolas Trangez]

On Tue, 2014-06-24 at 21:38 +0530, C K Kashyap wrote:
> Dear cafe,
> 
> I have created a reproducible app here -
> https://github.com/ckkashyap/haskell-perf-repro
> 
> Essentially I am trying to open a number of files and printing out their
> sized by reading them in and computing it's length.
> 
> I have the equivalent perl program also there. I'd appreciate it very much
> if someone could take a look at my Haskell implementation and point out
> what I am doing wrong. Since it's over 50 times slower than the perl code,
> I assume I am doing something obviously incorrect.

That's simply because your Haskell program is doing something completely
different than your Perl code.

Using `String` is the biggest offense. You're creating huge lists of
`Char`s instead of working on arrays of bytes, like your Perl code does.

I made some trivial changes to bring the Haskell code on par with your
Perl code speed-wise at
https://github.com/NicolasT/haskell-perf-repro/compare/ckkashyap:master...master Check it out!

Nicolas