[Haskell-cafe] Re: static constants -- ideas?
Don Stewart
dons at galois.com
Mon Mar 3 17:22:59 EST 2008
jason.dusek:
> I have an awkward programming problem -- I need to take a
> dictionary, parse it, build a bunch of intermediate lists and
> then make maps and tries out of the list. A "programming
> problem" because it's taken me a fair amount of effort to pull
> together the parser and list generator -- and "awkward"
> because a 69000 item list, [(String, [(String, String)])],
> does not compile under GHC (stack overflow). (It's not likely
> to compile under anything else, either!)
Here's an example of the approach Bryan outlined, which does seem to
work for files as large as gcc can handle:
* generate your big Haskell Map
* serialise it with Data.Binary, and Codec.Compression.GZip to a file
* compile the data into a C const array, and link that into Haskell
* decode it on startup, ressurecting the Haskell data.
The C source looks like:
const uint8_t beowulf[] = {
31, 139, 8, 0, 0, 0, 0, 0, 0, 3, 124, 189, 75,
150, 46, 54, 93, 193, 96, 144, 241, 168, 172, 238, 214, 0,
...
http://code.haskell.org/~dons/code/compiled-constants/cbits/constants.c
which is the gzip, Data.Binary encoded version of a Map ByteString Int.
Then the Haskell code need only access this array as a Ptr Word8, wrap
that as a Bytestring, then run Data.Binary over the result to rebuild
the Map. As you can see here:
http://code.haskell.org/~dons/code/compiled-constants/Constants.hs
I've put a couple of examples of how to access C-side serialised Haskell
values in a package here:
http://code.haskell.org/~dons/code/compiled-constants/
Cheers,
Don
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