[Haskell-cafe] why does the binary library require so much memory?
dons at galois.com
Fri Jul 31 17:27:30 EDT 2009
> On Fri, Jul 31, 2009 at 1:56 PM, Jeremy Shaw <jeremy at n-heptane.com> wrote:
> Using encode/decode from Binary seems to permamently increase my
> memory consumption by 60x fold. I am wonder if I am doing something
> wrong, or if this is an issue with Binary.
> It's an issue with the Binary instance for lists, which forces the entire spine
> of the list too early. This gives you a gigantic structure to hold onto.
This is the current instance
instance Binary a => Binary [a] where
put l = put (length l) >> mapM_ put l
get = do n <- get :: Get Int
-- | 'getMany n' get 'n' elements in order, without blowing the stack.
getMany :: Binary a => Int -> Get [a]
getMany n = go  n
go xs 0 = return $! reverse xs
go xs i = do x <- get
-- we must seq x to avoid stack overflows due to laziness in
x `seq` go (x:xs) (i-1)
It used to be this, though,
xs <- replicateM n get -- now the elems.
More information about the Haskell-Cafe