[Haskell-cafe] The where-clause and guards

[Eitan Goldshtrom]

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
>