[Haskell-cafe] Linking in Large ByteStrings

Judah Jacobson judah.jacobson at gmail.com
Fri Jan 1 16:19:42 EST 2010

On Fri, Jan 1, 2010 at 7:09 AM, Tom Hawkins <tomahawkins at gmail.com> wrote:
> I have a large tarball I want to link into an executable as a
> ByteString.  What is the best way to do this?  I can convert the
> tarball into a haskell file, but I'm afraid ghc would take a long time
> to compile it.  Is there any way to link constant data directly with
> ghc?  If not, what's the most efficient way to code large ByteStrings
> for fast compilation?

Possibly the simplest is to use unsafePackAddress or unsafePackAddressLen:

{-# LANGUAGE MagicHash #-}
module Const where

import Data.ByteString.Unsafe as U
import System.IO.Unsafe
my_bstr = unsafePerformIO $ U.unsafePackAddress  "abcdefg"#

This trick of embedding raw strings (of type Addr#) is how happy and
alex store their parser lookup tables in the modules they generate.
I haven't seen any performance issues with it myself.

Hope that helps,

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