Hal Daume III wrote:
I have a datatype which (simplified) looks like:
data FBTree a = FBLeaf (Maybe (FBTree a)) a | FBBranch (Maybe (FBTree a)) (FBTree a) (FBTree a)
is basically a tree with Maybe a parent node. however, unlike the nice non-haskell equivalent, they tend to eat up memory as you traverse them.
Oh no they don't! :-) There is no space leak in the tree-traversal part of Hal's program, the problem is that the program builds an iterated sequence of ever-deeper compositions of findRoot and findLeftMostChild without demanding any of their results until the very end of the sequence. Quick plug: heap profiling showed me that the problem was with iterate; the Hat tracing tools showed me that the tree traversal routines work fine. I attach an amended version of Hal's program which does the 100000 down-up traversals without leaking. Regards Colin R data Tree a = Leaf a | Branch (Tree a) (Tree a) deriving (Eq, Show) data FBTree a = FBLeaf (Maybe (FBTree a)) a | FBBranch (Maybe (FBTree a)) (FBTree a) (FBTree a) normalFBTree (FBLeaf _ _) = True normalFBTree (FBBranch _ _ _) = True instance Show a => Show (FBTree a) where showsPrec i = showsPrec i . unFBTree mkFBTree = mkFBTree' Nothing where mkFBTree' par (Leaf a) = FBLeaf par a mkFBTree' par (Branch l r) = this where this = FBBranch par (mkFBTree' (Just this) l) (mkFBTree' (Just this) r) unFBTree (FBLeaf _ a) = Leaf a unFBTree (FBBranch _ l r) = Branch (unFBTree l) (unFBTree r) findRoot (FBLeaf (Just par) _) = findRoot par findRoot (FBBranch (Just par) _ _) = findRoot par findRoot t = t findLeftMostChild (FBBranch _ l _) = findLeftMostChild l findLeftMostChild t = t tree = Branch (Branch (Branch (Branch (Branch (Leaf 'h') (Branch (Leaf 'a') (Leaf 's'))) (Leaf 'k')) (Branch (Leaf 'e') (Leaf 'l'))) (Leaf 'l')) (Leaf '!') fbtree = mkFBTree tree updown n t | normalFBTree t = if n > 0 then updown (n-1) (findLeftMostChild (findRoot t)) else t main = print (updown 100000 fbtree)