Ugh, my formatting got eaten up by gmail. I just removed the where in front of "m =", and aligned tat statment with your ballFold definition. I would also align the first where statement with the case bars of traceRay.
Nick On Wed, Jul 21, 2010 at 8:53 AM, Nicolas Wu <nicolas...@gmail.com> wrote: > As I understand the use of where clauses in [1], "A where clause is only > allowed at the top level of a set of equations or case expression", would > mean that the first "where" is scoping over the whole traceRay function: the > "where m =" shouldn't be there, since there's already a where clause in scope. > > Try this: > > traceRay (x,y) r@((cx,cy,cz):n) (vx,vy,vz) iter > | m > 100 = do > color $ Color3 (sin vx) (cos vy) (cos vz) > vertex $ Vertex2 x y > | otherwise = do > [boxx,boxy,boxz] <- boxFold [vx,vy,vz] > (ballx,bally,ballz) <- ballFold (boxx,boxy,boxz) > traceRay (x, y) r (2*ballx + cx, 2*bally + cy, 2*ballz + cz) (iter-1) > where > boxFold [] = return [] > boxFold (a:b) > | a > 2 = do > rem <- boxFold b > return $ (2-a):rem > | a < (-2) = do > rem <- boxFold b > return $ (-2-a):rem > |otherwise = do > rem <- boxFold b > return $ (a):rem > ballFold (x,y,z) > | n < 0.5 = return (4*x, 4*y, 4*z) > | n < 1 = return (x/(n*n), y/(n*n), z/(n*n)) > | otherwise = return (x, y, z) > where n = sqrt $ x*x + y*y + z*z > m = sqrt $ vx*vx + vy*vy + vz*vz > > > > [1] http://www.haskell.org/tutorial/patterns.html > > On Wed, Jul 21, 2010 at 8:38 AM, Eitan Goldshtrom <thesource...@gmail.com> > wrote: >> Well, perhaps you can help me figure out the problem with my exact program. >> Just in case it matters, the program draws a Mandelbox via volumetric ray >> casting. I can provide more information about the function, but I wouldn't >> think it's necessary, since my problem is with parsing. The error I'm >> getting is with the where-clause at the very bottom: >> >> traceRay (x,y) r@((cx,cy,cz):n) (vx,vy,vz) iter >> | m > 100 = do >> color $ Color3 (sin vx) (cos vy) (cos vz) >> vertex $ Vertex2 x y >> | otherwise = do >> [boxx,boxy,boxz] <- boxFold [vx,vy,vz] >> (ballx,bally,ballz) <- ballFold (boxx,boxy,boxz) >> traceRay (x, y) r (2*ballx + cx, 2*bally + cy, 2*ballz + cz) (iter-1) >> where >> boxFold [] = return [] >> boxFold (a:b) >> | a > 2 = do >> rem <- boxFold b >> return $ (2-a):rem >> | a < (-2) = do >> rem <- boxFold b >> return $ (-2-a):rem >> |otherwise = do >> rem <- boxFold b >> return $ (a):rem >> ballFold (x,y,z) >> | n < 0.5 = return (4*x, 4*y, 4*z) >> | n < 1 = return (x/(n*n), y/(n*n), z/(n*n)) >> | otherwise = return (x, y, z) >> where n = sqrt $ x*x + y*y + z*z >> where m = sqrt $ vx*vx + vy*vy + vz*vz >> >> On 7/21/2010 3:13 AM, Nicolas Wu wrote: >>> >>> There's nothing wrong with the use of your example, I'm guessing it's >>> something in your ... that's leading to the parse error. This compiles >>> just fine: >>> >>> f a b >>> | c> 1 = 1 >>> | c< 1 = 2 >>> | otherwise = 3 >>> where c = a+b >>> >>> Nick >>> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
