The compiler is complaining that there's no instance of the Floating class for Int because Floating is the class where pi and tan are defined, and it manages to infer that halfWidth must be an Int. How does it do this? Well, assuming that you are using SOE or a similar graphics library, the polygon function expects a list of Points, and type Point = (Int, Int). So, in particular, x1 - halfWidth must be an Int, and so halfWidth needs to be an Int. Hence, you probably want to change the definition of halfWidth to be: halfWidth = round (height * tan (pi / 3)) Also, just as a side note, your indentation is a little unusual. It's more common to align the 'let' with the 'in'. This would also be an appropriate place to use 'where'. hope this helps, - Cale On 12/10/06, Edward Ing wrote:

Hi, I am new to Haskell, so the following problem is probably easy for you to spot but difficult for me. Any pointers would be appreciated. In GHCI on a load I am getting the following message:

SSnowflake.hs:41:45: No instance for (Floating Int) arising from use of `pi' at Snowflake.hs:41:45-46 Probable fix: add an instance declaration for (Floating Int) In the first argument of `(/)', namely `pi' In the first argument of `tan', namely `(pi / 3)' In the second argument of `(*)', namely `(tan (pi / 3))' Failed, modules loaded: none.

When I put the expression "tan ( pi / 3)" at the GHCI interpreter prompt I get a value, but this is not accepted on a load the code.

Here is the code:

...

...

...

...

code

triangle :: Window -> (Point,Point) -> Int -> IO () triangle window ((x1,y1), (x2,y2)) size = let height = fromIntegral(y2 - y1) * 3 / 2 halfWidth = height * (tan (pi / 3 )) in drawInWindow window (withColor (sizeColorMap size) (polygon [(x1,y1),( x1 - halfWidth, height ), (x1 + halfWidth, height)] ))

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Am Freitag, 13. Oktober 2006 02:22 schrieb Edward Ing:

Hi, I am new to Haskell, so the following problem is probably easy for you to spot but difficult for me. Any pointers would be appreciated. In GHCI on a load I am getting the following message:

SSnowflake.hs:41:45: No instance for (Floating Int) arising from use of `pi' at Snowflake.hs:41:45-46 Probable fix: add an instance declaration for (Floating Int) In the first argument of `(/)', namely `pi' In the first argument of `tan', namely `(pi / 3)' In the second argument of `(*)', namely `(tan (pi / 3))' Failed, modules loaded: none.

When I put the expression "tan ( pi / 3)" at the GHCI interpreter prompt I get a value, but this is not accepted on a load the code.

Here is the code:

...

...

...

...

code

triangle :: Window -> (Point,Point) -> Int -> IO () triangle window ((x1,y1), (x2,y2)) size = let height = fromIntegral(y2 - y1) * 3 / 2 halfWidth = height * (tan (pi / 3 )) in drawInWindow window (withColor (sizeColorMap size) (polygon [(x1,y1),( x1 - halfWidth, height ), (x1 + halfWidth, height)] ))

The co-ordinates must have type Int, I believe, tan has type Floating a => a -> a. However, Int is not an instance of the Floating class. What you ought to do is convert height and halfWidth to Int via round, floor or ceiling. Then it should work. Cheers, Daniel

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