[Haskell] A few newbie questions about tracing/debugging and order of execution

[Robert Dockins]

On Dec 28, 2005, at 12:07 PM, Hunter Kelly wrote:

> Yes, thank you, that did the trick!  It produced the output for all  
> steps,
> and in the order I would expect.
>
> Are there other techniques that people use to get debugging output?
>

Well, if you are writing code in the IO monad, obviously you can just  
insert 'putStrLn', just like in your favorite imperative language.   
For pure code, I generally try to write small functions and then  
compose them to do larger tasks.  That way I can exercise each  
smaller function individually and see that I get the results I  
expect.  It is also more likely that your functions will just be  
"obviously correct".

If that isn't possible for some reason I go to Debug.Trace and try to  
find good places to sprinkle in the calls to 'trace'.  I find that  
attaching them to control structures usually works best.

If that doesn't cut it for you, there are also some interactive  
Haskell debuggers. (http://www.haskell.org/libraries/#tracing).



Rob Dockins

Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
           -- TMBG