"Neil Mitchell"
Hi
Yes, and if the compiler is this clever, it should also be free to replace them back at debug time.
And where does that get us? You snipped the salient bit where I said that you'd be debugging a different programme.
In Visual C there are two compilation modes. In debug mode, if you create a variable "i" it WILL be there in the compiled version. It won't be merged with another variable. It won't be constant folded. It won't have its value globablly computed and stored. It won't be placed only in the register. In release mode all these things can (and do) happen. I'm not saying Haskell compilers aren't free to optimize, but maybe there is a need for one that is this "debug mode" style.
I think this chiefly indicates that you think of variables as things, which in Haskell they are not.
At no point have I ever used a debugger on a Haskell programme.
Because you couldn't find a working debugger? ;) If one had been there, just a click away, would you never have been tempted?
Not in the least. The highest level language I've ever wanted to use a debugger on was C, and that was for debugging a pointer-reversing garbage collector, which ties in with what Andrae says.
Let take for example a bug I spent tracking down in Haskell this weekend. The bug can be summarized as "Program error: pattern match failure: head []". And indeed, thats all you get. A quick grep reveals there are about 60 calls to head in the program. In this instance I have the choice between 1) crying, 2) a debugger, 3) a lot of hard work. [Of course, knowing this situation arises, I had already prepared my getout plan, so it wasn't a massive problem]
H'm. I've never been completely convinced that head should be in the language at all. If you use it, you really have to think, every time you type in the letters h-e-a-d, “Am I /really/ /really/ sure the argument will never be []?” Otherwise you should be using a case expression or (more often, I think) a subsidiary function with a pattern match. Most of the occurrences of “head” in my code seem to be applied to infinite lists, or commented out, or rebindings of head to something else, sloppy bits of nonce programming or references in comments to the top of my own noddle. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2006-07-14)