Daniel, On 10/27/2011 03:26 PM, Daniel Fischer wrote:
On Thursday 27 October 2011, 15:44:34, Hugo Ferreira wrote:
My apologies, the 2nd function should be:
scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs where scoreElem r s@(nCorrect, nIncorrect) z = case ruleApplication r z of Just tag -> if tag == correct then let nCorrect = nCorrect + 1 in
This is a cyclic definition. The nCorrect on the right hand side is not the nCorrect from the function parameter but the nCorrect from the left hand side of the definition, so you have a nonterminating value here. You need to introduce a new name,
let newCorrect = nCorrect + 1 in newCorrect `seq` (newCorrect, nIncorrect)
That was unexpected. I assumed a new variable with the same name.
(since nIncorrect isn't changed, we don't need to use seq on that).
Ok. Understood. But something seems to be wrong here. If I do: scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs where scoreElem r s z = let (nCorrect, nIncorrect) = s in case ruleApplication r z of Just tag -> if tag == correct then (nCorrect+1, nIncorrect) else (nCorrect, nIncorrect+1) Nothing -> (nCorrect, nIncorrect) where c = Z.cursor z (correct,_) = c it works correctly, however this does not work: scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs where scoreElem r (!nCorrect, !nIncorrect) z = case ruleApplication r z of Just tag -> if tag == correct then (nCorrect+1, nIncorrect) else (nCorrect, nIncorrect+1) Nothing -> (nCorrect, nIncorrect) where c = Z.cursor z (correct,_) = c I have been staring at this for some time now, but cannot understand why it does not work. Any ideas? Regards, Hugo F.
nCorrect `seq` nIncorrect `seq` (nCorrect, nIncorrect) else let nIncorrect = nIncorrect + 1 in
Same problem here.
nCorrect `seq` nIncorrect `seq` (nCorrect, nIncorrect) Nothing -> s where (correct, _) = Z.cursor z
R, Hugo F.
On 10/27/2011 02:22 PM, Hugo Ferreira wrote:
Hello,
After trying the suggestions, I still cannot execute the code. I have tried:
scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs where scoreElem r !s@(!nCorrect, !nIncorrect) z = case ruleApplication r z of Just tag -> if tag == correct then (nCorrect+1, nIncorrect) else (nCorrect, nIncorrect + 1) Nothing -> s where (correct, _) = Z.cursor z
That should run, what's the problem here? Perhaps the bangs should be placed s@(!(InCorrect, !nIncorrect)), I'm not sure how ghc treats bang patterns exactly atm.
and
scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs nIncorrect) where (correct, _) = Z.cursor z nCorrect = nCorrect + 1 nIncorrect = nIncorrect + 1
Again cyclic definitions.
where scoreElem r s@(nCorrect, nIncorrect) z = case ruleApplication r z of Just tag -> if tag == correct then let nCorrect = nCorrect + 1 in nCorrect `seq` nIncorrect `seq` (nCorrect, nIncorrect) else let nIncorrect = nIncorrect + 1 in nCorrect `seq` nIncorrect `seq` (nCorrect, nIncorrect) Nothing -> s where (correct, _) = Z.cursor z
Here too.
In an attempt to figure out the problem I also tried:
scoreRule_ r zs = Z.foldlz' (scoreElem r) (0, 0) zs where scoreElem r !s@(!nCorrect, !nIncorrect) z = (nCorrect, nIncorrect) where (correct, _) = Z.cursor z nCorrect = nCorrect + 1 nIncorrect = nIncorrect + 1
Strangely enough GHC complains that correct, nCorrect and nIncorrect are not used.
With -Wall or -fwarn-name-shadowing it should also complain about the shadowing of nCorrect and nIncorrect.
Why is this so for nCorrect and nIncorrect? Why won't the above also execute in a strict manner?
Does anyone have any ideas why I still get stack-overflow?
TIA, Hugo F.