[Haskell-beginners] parallel map/filter

[Csaba Marosi]

Thanks for the tips, some comments:
a) I tried to print the list before my expensive map (prints fast) and
even copy-paste the content into the source code, but it did not help.
b) What do you mean by this?

One more question: when I run my program with -s, the stats:
   4,961,037,352 bytes allocated in the heap
      19,431,024 bytes copied during GC
[...]
               3 MB total memory in use (0 MB lost due to fragmentation)

What does the first number (~ 5G memory) mean? When I wrote my
functions, I just assumed that even the bad code will be fast enough.
(Even this question is more about learning that a practical issue.)
Can you recommend any docs about this kind of Haskell internals?

PS: splitting the input file to two, and use bash to wait both half
reduces the runtime by ~40%. What I want here is to annotate my
program with this knowledge to help ghc to beat bash :)


On 6/5/15, Marcin Mrotek <marcin.jan.mrotek at gmail.com> wrote:
> My first guesses would be that:
> a) Your program is slowed down because lines from the file is read one line
> by one, i.e. there's lazy IO at work. Have you tried your code on a list
> that's loaded in the memory as a whole at once?
> b) The cost of dereferencing the next link in a list overwhelms the cost of
> computing one answer. Have you tried using a tree instead?
>
> Best regards,
> Marcin Mrotek
>