Hi,
i wrote a program that doesn't behave as i wanted.
So i tried to putStrLn my data structures to see what happened. Since i
did this, all my functions changed type, so i had to modify them (main
and calcul : use <- instead of let , add returns) and so on for each
function called. Debugging this way causes more trouble than it should
save.
What is the way to trace data thru function recursive calls without
changing program structures? Is putStrLn a good idea ?
I'm not used to ghci debug and i find it hard to manage (:break, :trace,
:cont ...).
Is the 'debugged' version as efficient as the first one, due to impure
functional code? What if i want to remove 'debug code' ? Should i
modify back my functions ?
Here are two very simplified versions of my program, the first one
without 'trace', the second modified to include putStrLn as wanted.
Thanks in advance,
Didier
First version
-------------
main=do
let valeurs=[0,1,3,0]
let (valeurs_new)=calcul valeurs
afficher_resultat valeurs
afficher_resultat valeurs_new
calcul :: [Int] -> [Int]
calcul xv
| nblibr == 0 = map (*2) xv
| otherwise = map (+1) xv
where
libres = [ x | x <- [1..length xv] , xv !! (x-1) == 0]
nblibr=length libres
afficher_resultat xv = do
putStrLn (show xv)
Second version
----------------
main=do
let valeurs=[0,1,3,0]
valeurs_new <- calcul valeurs
afficher_resultat valeurs
afficher_resultat valeurs_new
calcul :: [Int] -> IO [Int]
calcul xv
| nblibr == 0 = do
putStrLn "ok"
return (map (*2) xv)
| otherwise = return (map (+1) xv)
where
libres = [ x | x <- [1..length xv] , xv !! (x-1) == 0]
nblibr=length libres
afficher_resultat xv = do
putStrLn (show xv)
