I haven't tried to run the code, but my first bet is that, due to the rank-2 polymorphism of ST, you should use parenthesis instead of $ in the case of runST. On Sun, Aug 24, 2008 at 3:25 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:
colour_grid :: (Particle -> IO ()) -> Grid ph -> IO () colour_grid fn g = sequence_ $ runST $ do ps <- grid_coords g
mapM (\pix -> do particle <- read_grid g pix return $ fn particle ) ps
When I attempt to run this, GHCi just gives me a very cryptic type checker error. I can't figure out what's wrong here. As far as I can tell, this should run...
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