Hi, I don't understand why the following code always result in a Stack space overflow error. I'm using foldl' and think the main algorithm is tail recursive. Am I wrong ? I've read the http://www.haskell.org/haskellwiki/Stack_overflow Any help would be greatly appreciated. Thanks module Main where import Data.List -- Data structures data Point = Point { x::Double, y::Double, z::Double } deriving(Eq, Show) data Triangle = Triangle { p1::Point, p2::Point, p3::Point } deriving(Eq, Show) data BBox = BBox { bbmax::Point, bbmin::Point } deriving(Eq,Show) -- Construct a default triangle newTriangle :: Triangle newTriangle = Triangle (Point 1 0 0) (Point 0 1 0) (Point 0 0 1) -- Construct a default BBox newBBox = BBox (Point 0 0 0) (Point 0 0 0) -- Defines min and max for Point instance Ord Point where max a b = Point ( max (x a ) (x b) ) ( max (y a) (y b) ) ( max (z a) (z b) ) min a b = Point ( min (x a ) (x b) ) ( min (y a) (y b) ) ( min (z a) (z b) ) -- Create a list of triangles makeTriangles :: Double -> [Triangle] makeTriangles 0 = [] makeTriangles n = [ Triangle (Point v 0 0) (Point 0 v 0) (Point 0 0 v) | v <- [1..n] ] -- Compute the bounding box of a triangle boundingBox :: Triangle -> BBox boundingBox t = BBox pmax pmin where pmax = max (p3 t) (max (p1 t) (p2 t)) pmin = min (p3 t) (min (p1 t) (p2 t)) -- Compute the bounding box of two bounding boxes bboxAddb :: BBox -> BBox -> BBox bboxAddb (BBox bb1max bb1min) (BBox bb2max bb2min) = BBox (max bb1max bb2max) (min bb1min bb2min) -- Compute the bounding box of a triangle and a bounding box bboxAddt :: BBox -> Triangle -> BBox bboxAddt b t = bboxAddb b (boundingBox t) main = do print $ foldl' bboxAddt newBBox triangles; where triangles = makeTriangles 610000 error returned : Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. ghc version 6.10.3 on MacOsX Snow Leopard