On Wednesday 22 June 2005 06:38 pm, Andrew Ward wrote:
% This general pattern of dynamic binding I use over and over again. Could
% you give me some example code of this type of thing handled in Haskell's
% way? Assuming that the number of classes deriving from shape might get
% quite large.
What is "large"? Less than, say, 30? If so:
> module Shapes where
> type Position = (Float, Float)
> data Shape = Circle Position Float
> | Square Position Float
> prim_draw_circle x y radius =
> return ("circle(" ++ show x ++ ", " ++ show y ++ ", " ++
> show radius ++ ")")
>
> prim_draw_rect x0 y0 x1 y1 =
> return ("square(" ++ show x0 ++ ", " ++ show y0 ++ ", " ++
> show x1 ++ ", " ++ show y1 ++ ")")
> draw :: Shape -> IO String
> draw (Circle (x, y) radius) = prim_draw_circle x y radius
> draw (Square (x, y) size) = prim_draw_rect x y (x+size) (y+size)
> drawShapes :: [Shape] -> IO String
> drawShapes (x:xs) = do s <- draw x
> putStrLn s
> drawShapes xs
> drawShapes [] = return ""
> shapes = [ Circle (0.0, 0.0) 1.0,
> Circle (1.0, 1.0) 2.0,
> Square (0.0, 0.0) 2.0 ]
> main = drawShapes shapes
PKE.
--
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\`. Pål-Kristian Engstad, Lead Programmer,
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