Stefan O'Rear wrote:
I like pretty pictures.
...and have lots of spare time, apparently. ;-) [I actually meant to write (Bool,Bool), but anyway...]
Whereas my Quad object is going to be a pointer to one of 4 values... so it looks like Quads save space. (And they're more strict.) OTOH, I'm not sure what the time penalty is like...
Probably none. The STG-machine was designed to make user-defined algebraic types very fast.
My program needs to make decisions based on a pair of boolean values. Encoding both values as a single algebraic data type means I have to keep "taking it apart" so I can work with it. I'm not sure how much time this wastes...
It would be nice if there were some general mechanism for turning a bunch of Bool flags into a single machine word. E.g., if I did a
data Foo = Foo {flagX, flagY, flagZ :: !Bool}
and it ends up that a Foo value is just a single machine word, and GHC picks which bit each flag is... I guess if you want that at present you'd have to code it all by hand. Hmm, I think this might work out better than my current Quad thing... I could do something like
type Quad = Word8
foo q = let x = if testBit 0 q ... y = if testBit 1 q ...
That should be quite fast... (?)
Probably. I wound up doing something similar with vty, to considerable gain. (I did however use .&. instead of testBit - probably makes no difference, but I'm reminded of the (^2) being much slower than join(*) case...)
Well, perhaps I could define a pair of constants representing the bit masks? (OTOH, won't GHC optimise "testBit <constant>" into something faster anyway?)
Heh. I'll have to pester you more often. :-P
:)
Like that time yesterday, I compiled from program and got a weird message about GHC about "ignored trigraphs" or something... What the heck is a trigraph? (I compiled the program again later, and it compiled just fine. Weird...)
PS. Somewhere they should write a page entitled "Optimisations that GHC does (and doesn't) do"...
Good idea! Maybe it could be fit into the GHC Performance Resource somehow? (http://www.haskell.org/haskellwiki/Performance/GHC)
OK. But it'll probably contain a lot of guessing to start with... ;-)