HAVE_LIBM test doesn't work

[donn]

The AC_SEARCH_LIBS test in configure.ac will always set HAVE_LIBM=1, whether the platform supports -lm or not. It's really testing whether atan works, and it will indeed normally work -- the question is just whether it requires an explicit -lm. The mechanics of this can be seen in the generated configure script: look for "none required".

The preceding test for HAVE_MINGWEX does work, and of course that formula works for HAVE_LIBM too.

[igloo]

If we're always setting HAVE_LIBM=1, is there a reason not to drop the test and just always use -lm?

[donn]

Yes, we aren't always setting HAVE_LIBM=1. GHC won't build on my platform unless I fix this. I can't believe it's the only such platform, -lm always seemed to me like a nuisance that you'd have only for the sake of extreme '70s period authenticity.

It's a simple fix - use CHECK_LIB, just like with mingwex right above it.

[igloo]

Replying to donn:

Yes, we aren't always setting HAVE_LIBM=1

Do you mean "we shouldn't be always setting HAVE_LIBM=1"?

What is your platform?

[donn]

I mean, "we're either not setting HAVE_LIBM=1, or we're not building GHC on my platform."

The platform is Haiku, which inherited this practice from BeOS.

[igloo]

Fixed:

Thu Aug  5 15:25:08 BST 2010  Ian Lynagh <igloo@earth.li>
  * Fix the -lm configure test; fixes #4155