[Haskell-beginners] Performance of parallel mergesort

[Chaddaï Fouché]

On Thu, Dec 24, 2009 at 10:09 AM, Tom Davie <tom.davie at gmail.com> wrote:
> The mergesort example given here has a rather nasty problem – it creates
> sparks for mergeing the two lists at the same time as it creates the lists,
> so there's always at least one task blocking waiting for it's producers.

Don't worry too much about this thread, here is why :

- Jon Harrop is definitely not a beginner in Haskell land and has no
business asking this question on this list
- Jon Harrop is very well known on established functional programming
mailing lists and forum as a very disagreeable troll (not only on
Haskell). He love to trash whatever language hasn't his favours at the
moment (I think right now he likes F#, which is a very interesting
language nonetheless).
- He apparently made an effort to include approximately all elements
that could hurt Haskell reputation in this thoughtful gift to the
community in this Christmas period :
** As you pointed the initial code he chose doesn't parallelize very
well basically
** He tried to compile it with GHC 6.8 which was an important step
towards better internals to handle parallelism in GHC but was also a
time of big upheaval in this field and so not as stable as one could
wish.
** He then installed GHC 6.10 and did not even clean up his previous
compilations attempts before declaring that it didn't work (the error
message he cited is usually observed when GHC encounters an interface
file created by a previous version of GHC or on another architecture)
at all without testing on some other clean sources.
** He then apparently decided that using a binary package for the 6.12
version was beneath its dignity and went on to install it from source
(generally not recommended except for GHC developers that needs to
work on the code or for port to unusual architectures) and claimed
that there was a "circularity problem" since its 6.10 could not
compile it (which it obviously could, as he discovered and qualified
as "miraculous", not even considering that he had a working 6.8
before).

I could choose to believe that Harrop really is as incompetent as he
sounds and really did encounter all those problems (which are all
possibles if unlikely to be met in quick succession) but the simple
fact that he decided to post this message on the Haskell-Beginner list
instead of the Haskell-cafe list where he's already well known and an
occasional poster makes it that much more unlikely. The other
interpretation is that JdH is up to his usual tricks, just sinking to
a new low by posting in a venue where he's less likely to be
recognized and more likely to worry unwary would-be-haskell-beginners.

Merry Christmas !
-- 
Jedaï