# [Haskell-cafe] The where-clause and guards

Eitan Goldshtrom thesourceofx at gmail.com
Wed Jul 21 03:38:29 EDT 2010

```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
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
>
```