unboxed types

[Simon Marlow]

Ian Lynagh wrote:
> On Mon, Dec 31, 2007 at 09:14:04AM -0500, Isaac Dupree wrote:
>> I guess boxed types are too risky for efficiency reasons in some parts 
>> of the code
> 
> Again, I'd hope that that isn't true for modern GHC, and I personally
> would love to see less unboxed hackery in GHC's sources; I think it
> sends a bad message: that this sort of thing is necessary to get good
> performance.

It's true that unboxed types aren't necessary to get good performance. 
However, much as I hate to say it, they're necessary to *reliably* get good 
performance.  When I write code that uses unboxed types, I know I never 
have to worry about some fragile property being broken when someone tweaks 
the code in the future, leading to a performance regression that we 
probably won't notice for ever.

When I optimise things, I like them to stay optimised.

Similar problems arise with space leaks.  Several times I've profiled GHC 
and eliminated a bunch of space leaks, and invariably the leaks come back 
again, so now I've given up on fixing all but the really bad ones.  One day 
I'll add an ASSERT_UNREACHABLE predicate...

Cheers,
	Simon