BTW, this is a case where it may be more convenient to use forM: forM ps $ \pix -> do particle <- read_grid g pix return $ fn particle (untested...) forM is just another way of saying (flip mapM). / Emil Andrew Coppin skrev:
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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