Dynamic linking
By default, Haskell executables are statically linked. Most of the time this is fine, but static linking can become a problem when you go to build your test suite and wind up with an executable like this:
justin@ubuntu:~$ ./huskc t-basic.scm
...
justin@ubuntu:~$ ls -l t-basic
-rwxrwxr-x 1 justin justin 42357805 2012-02-16 14:38 t-basic
That’s right, a 42 megabyte executable for a program that just consists of a few unit tests! But it is possible to enable dynamic linking with a bit of effort. The main catch is that we need to recompile each of the packages that husk depends on:
cabal update
cabal install mtl transformers utf8-string terminfo text \
parsec haskeline --enable-shared --reinstall
cabal install husk-scheme --enable-shared --reinstall
The key thing to remember is the --enable-shared directive which builds a shared library. Fortunately the base packages already come with shared libraries so they do not need to be recompiled.
Anyway, now let’s rebuild that test suite. The -d flag is a new feature in version 3.5.3 that instructs huskc to create a dynamically linked executable:
justin@ubuntu:~$ huskc -d t-basic.scm
...
justin@ubuntu:~$ ls -l t-basic
-rwxrwxr-x 1 justin justin 2935380 2012-02-16 14:39 t-basic
With dynamic linking our compiled executable is now less than 3 megs. And it can be made even smaller by stripping out unnecessary debug information:
justin@ubuntu:~$ strip -p --strip-unneeded --remove-section=.comment -o t-basic-small t-basic
justin@ubuntu:~$ ls -l
...
-rwxrwxr-x 1 justin justin 2935380 2012-02-16 14:39 t-basic
-rwxrwxr-x 1 justin justin 2074536 2012-02-16 14:39 t-basic-small
So we took an executable that was orginally over 42 megs, and managed to strip it down all the way to 2 megs. Not bad!
Now that said, most of the time static linking is good enough, and is convenient since this is how everything works out-of-the-box. But it is good to have a work-around when you need it.