Hello, I was playing around with "bang patterns" and I noticed that when combined with asynchronous exceptions they can lead to programs where the order of the declarations in a binding group is important! Here is an example:
> import Control.Exception > import Prelude hiding (catch) > > main = putStrLn =<< eval_order > > test = "no exception" > where !_ = error "top down" > !_ = error "bottom up" > > eval_order = evaluate test `catch` \e -> > case e of > ErrorCall txt -> return txt > _ -> throw e Of course, this is a contrived exampled but, as far as I know, this was not possible in Haskell before (if anyone has an example to the contrary please send it to the list). By the way, with GHC 6.8.1 the above program prints "bottom up". This means that when there are multiple "banged" bindings they are evaluated starting with the last one in the text. I imagine than in most programs this is not particularly important, but it seems to me that it would be a bit nicer if we were to adjust the translation so that bindings were evaluated top to bottom (e.g., like in ML). Finally, the above program is accepted by GHC 6.8.1 without any special flags (e.g., no need for -XBangPatterns). Is this intentional? -- Iavor _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
