[Haskell-cafe] Removing alternate items from a list

Markus Läll markus.l2ll at gmail.com
Wed Jun 9 16:47:32 EDT 2010

So out of curiosity i took the definitions given in this thread, and
tried to run timing-tests.
Here's what I ran:
> ghc -prof -auto-all -o Test Test.h
> Test +RTS -p
and then looked in the Test.prof file.

All tests I ran from 3 to 10 times (depending on how sure I wanted to
be), so the  results are not entirely exact. (I copied the "average"
result to the source-file as comments above every function.)

As the function doing (x:_:rest) pattern-matching was the fastest I
extended the idea from that to (x1:_:x2: ... x10:_:rest), but skipping
from 5 to 10, where all steps showed a small increase in performance.

So a question: when increasing the pattern matched, is it somekind of
way of inlining the matchings, and if so, is there some way of just
saying that to the compiler how many recursions you want to inline
together to increase speed?

Any comments? (besides -O2 ;-)  -- I remembered it too late and didn't
want to restart... At least for the last two functions it showed a
similar difference in seconds as with no -O2)

Markus Läll

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