On 06/09/2006, at 8:22 PM, Neil Mitchell wrote:
It's been my experience that debugging is a serious weakness of Haskell - where even the poor mans printf debugging changes the semantics! And everyone comes up with arguments why there is no need to debug a functional language - that sounds more like excuses about why we can't build a good lazy debugger :)
[Sorry for the slight rant, but I've used Visual Studio C++ so I know what a good debugger looks like, and how indispensable they are]
I simply can't let this pass without comment. It's irrelevant if you're using a functional or imperative language, debuggers are invariably a waste of time. The only reason to use a debugger is because you need to inspect the contents of a processes address- space; so either you're using it as a disassembler, or you're using it to examine the consequences of heap/stack corruption. Consequently, if you're using Java, C#, Scheme, Haskell, Erlang, Smalltalk, or any one of a myriad of languages that don't permit direct memory access, there's no reason for you to be using a debugger. Jon understates it by implying this is a Functional/Haskell specific quality - it's not. Debuggers stopped being useful the day we finally delegated pointer handling to the compiler/vm author and got on with writing code that actually solves real problems. It's just that historically functional programmers have tended to already be experienced programmers who realise this. Why would they waste their time building a tool that no-one needs? It's a truism to say if your code doesn't work it's because you don't understand it; clearly if you did understand it, you wouldn't have included the bug that's causing you difficulty. Therefore either 1) The code is poorly structured and you need to restructure it to better represent your understanding of the problem or 2) Your understanding of the problem is flawed, so you need to sit back and reexamine your thinking on this problem in light of the counter-example you have found (the bug). Spending your time tracing through individual lines of code is counter-productive in both cases. Andrae Muys P.S. It is worth noting that I am here talking about the sort of debugger raised in the original post. I am not talking about using a separate tool to extract a stracktrace from a core file in a C/C++ program or equivalent - I'm talking about runtime debugging with variable watches, breakpoints, and line-by-line stepping. -- Andrae Muys andrae@netymon.com Principal Kowari Consultant Netymon Pty Ltd