My guess is that Cont plays really nicely with GHC's inliner, so things that
end up looking like
return x >>= \y -> ...
get optimized really well
return x >>= f
-- inline >>=
= ContState $ \s0 k -> runCS (return x) s0 $ \a s1 -> runCS (f a) s1 k
-- inline return
= ContState $ \s0 k -> runCS (ContState $ \s2 k2 -> k2 x s2) s0 $ \a s1
-> runCS (f a) s1 k
-- runCS record selector
= ContState $ \s0 k -> (\s2 k2 -> k2 x s2) s0 $ \a s1 -> runCS (f a) s1
k
-- beta
= ContState $ \s0 k -> (\k2 -> k2 x s0) $ \a s1 -> runCS (f a) s1 k
-- beta
= ContState $ \s0 k -> (\a s1 -> runCS (f a) s1 k) x s0
-- beta
= ContState $ \s0 k -> runCS (f x) s0 k
and then further inlining of f can take place.
On Mon, Sep 26, 2011 at 4:07 PM, Nicu Ionita
Hello list,
Starting from this emails (http://web.archiveorange.com/** archive/v/nDNOvSM4JT3GJRSjOm9Phttp://web.archiveorange.com/archive/v/nDNOvSM4JT3GJRSjOm9P **) I could refactor my code (a UCI chess engine, with complex functions, in which the search has a complex monad stack) to run twice as fast as with even some hand unroled state transformer! So from 23-24 kilo nodes per second it does now 45 to 50 kNps! And it looks like there is still some improvement room (I have to play a little bit with strictness annotations and so on).
(Previously I tried specializations, then I removed a lot of polimorphism, but nothing helped, it was like hitting a wall.)
Even more amazingly is that I could program it although I cannot really understand the Cont & ContT, but just taking the code example from Ryan Ingram (newtype ContState r s a = ...) and looking a bit at the code from ContT (from the transformers library), and after fixing some compilation errors, it worked and was so fast.
I wonder why the transformers library does not use this kind of state monad definition. Or does it, and what I got is just because of the unrolling? Are there monad (transformers) libraries which are faster? I saw the library kan-extensions but I did not understand (yet) how to use it.
Nicu
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