Re: [Haskell-cafe] The where-clause and guards

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 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 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