From an interview with Julian Seward, author of the superb Valgrind (as well as cacheprof, bzip2, and a co-author for the Glorious Glasgow Haskell Compiler: quite a remarkably productive fellow, huh?):

Valgrind is loaded with assertion checks and internal sanity checkers which periodically inspect critical data structures. These are permanently enabled. I don’t care if 5 percent or even 10 percent of the total run-time is spent in these checksóautomated debugging is the way to go. As a result, Valgrind almost never segfaultsóinstead it emits some kind of a useful error message before dying. That’s something I’m rather proud of.

Nice indeed; I wonder if programming languages of the future will be able to do automatic assertions of such data structures in their run-time systems. All you’d need is to annotate the structures with some simple boolean conditions, and the language can merrily check them whenever a garbage collection pass is executed (since programming languages of the future will all have automatic memory management, of course. Right? Helllllllo?)

And, one more little quote (sorry, I couldn’t resist):

Valgrind is only useful because C and C++ are such crappy programming languages.

A-men to that, Haskell brother. Snigger snigger snigger …