2008/11/22 David F. Place <[EMAIL PROTECTED]>: > On Sat, 2008-11-22 at 11:33 +0000, Thomas Schilling wrote: >> Be careful, though. This only works if there's a single constructor >> for your exception type. If there are multiple, you should write it >> like this: >> >> thing_to_try `catch` \(e :: MyErrorType) -> case e of MyError1 _ -> >> ..; MyError2 _ -> ... >> >> If you write `catch` (MyError1 ...) and a MyError2 is thrown, you will >> get a pattern match error exception. >> > > Since I am trying to replicate the behavior of errorCalls, I have only > the single constructor ErrorCall to worry about. I don't understand > though, how this works: I have a predicate > > errorCalls e@(ErrorCall _) = Just e > > In the following transcript it seems to work correctly even if something > beside ErrorCall is thrown. Passing NonTermination to errorCalls get a > type error as expected. Why does it work inside tryJust? > > > *Main> tryJust errorCalls $ print $ [] !! 23 > tryJust errorCalls $ print $ [] !! 23^JLeft Prelude.(!!): index > too large > > *Main> tryJust errorCalls $ print $ throw NonTermination > tryJust errorCalls $ print $ throw NonTermination^J*** > Exception: <<loop>>
It doesn't. The last line is printed by GHCi. Note the missing "Exception: " in the first call. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
