Watch how deeply things are indented. The definitions for polyArea should be indented to the same level as its type signature. Currently, they're indented a little more, so the first line of polyArea's definition is being treated as part of the type signature, which is why you're getting the error. GHC/GHCi/hugs should be telling you also what line the error happens on, which should be a good clue here :) - Cale On 19/02/06, Chatzianastassiou Achilleas wrote:

Hi everybody,

I have written some code for several shapes, and i get a compiling error:

parse error on input `:'

though I can't find where the error is...

data Shape = Ellipse Radius Radius | Polygon [Vertex]

deriving Show

type Radius = Float type Vertex = (Float, Float)

area :: Shape -> Float area (Rectangle s1 s2) = s1 * s2 area (RtTriangle s1 s1) = s1 *s2 /2 area (Ellipse r1 r2) = pi * r1 * r2 area (Polygon(v1:v2:v3:vs)) = triArea v1 v2 v3 + area(Polygon(v1:v3:vs)) area(Polygon _ ) = 0 area (Polygon(v1:vs')) = polyArea vs where polyArea :: [Vertex] -> Float polyArea(v2:v3:vs') = triArea v1 v2 v3 + polyArea(v3:vs') polyArea _ = 0

triArea :: Vertex -> Vertex -> Vertex -> Float triArea v1 v2 v3 = let a = distBeetween v1 v2 b = distBeetween v2 v3 c = distBeetween v3 v1 s = 0.5 * (a + b + c) in sqrt (s * (s - a) * (s - b) * (s - c))

distBeetween :: Vertex -> Vertex -> Float distBeetween (x1, y1) (x2, y2) = sqrt ((x1 - x2) ^ 2 + (y1 - y2) ^ 2)

Any suggestions?

Thanks in advance,

Skag55

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