I had similar experiences as you when attempting to write "high
performance Haskell"; the language makes you want to use high-level
abstracted functions but the optimizer (while amazing, to be honest)
seems to miss a few cases that it seems like it should hit.
The problem seems to be that the compiler is extremely good at
optimizing systems-level code, but that any "control-structure"
function needs to be extremely inlined to be successful. You might
try re-writing "sequence" or "foldM" a few different ways using the
same "test" function and see what you can get.
One thing that I notice about this code is that if you switch Right
and Left you will get the default behavior for the Either monad:
worldSceneSwitch point = case redSphere (0,50,0) 50 point of
v@(Left _) -> v
Right d1 -> case greenSphere (25,-250,0) 50 point of
v@(Left _) -> v
Right d2 -> Right $ d1 `min` d2
is the same as
worldSceneSwitch point = do
d1 <- redSphere (0, 50, 0) 50 point
d2 <- greenSphere (25, -250, 0) 50 point
Right (d1 `min` d2)
Here is the same concept using foldM:
minimumM (x : xs) = do
v0 <- x
foldM (return . min) v0 xs
worldSceneSwitch point = minimumM [
redSphere (0, 50, 0) 50 point,
greenSphere (25, -250, 0) 50 point
]
However, the performance here will be terrible if minimumM and foldM
do not get sufficiently inlined; you do not want to be allocating list
thunks just to execute them shortly thereafter.
-- ryan
On Sat, Jul 19, 2008 at 6:48 AM, Mitar <[EMAIL PROTECTED]> wrote:
> Hi!
>
> I had to change code somewhat. Now I have a function like:
>
> worldScene point = case redSphere (0,50,0) 50 point of
> v@(Right _) -> v
> Left d1 -> case greenSphere (25,-250,0) 50 point of
> v@(Right _) -> v
> Left d2 -> Left $ d1 `min` d2
>
> (Of course there could be more objects.)
>
> Any suggestion how could I make this less hard-coded? Something which
> would take a list of objects (object functions) and then return a
> Right if any object function return Right or a minimum value of all
> Lefts. But that it would have similar performance? If not on my GHC
> version (6.8.3) on something newer (which uses fusion or something).
> Is there some standard function for this or should I write my own
> recursive function to run over a list of object functions? But I am
> afraid that this will be hard to optimize for compiler.
>
> (It is important to notice that the order of executing object
> functions is not important so it could be a good candidate for
> parallelism.)
>
>
> Mitar
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>
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