On Sun, 2010-12-26 at 13:38 +0100, Maxime Henrion wrote: > On Sun, 2010-12-26 at 13:58 +0200, Roman Cheplyaka wrote: > > * Maxime Henrion <[email protected]> [2010-12-26 12:01:31+0100] > > > Anyone knows what I'm doing wrong here? I suspect my attempt at having > > > self-referential data is somehow buggy; do I need to treat transitions > > > to the same state differently? > > > > The problem is that when you call 'self', you record *that* state of > > your DFA in the map. When DFA gets updated further, the recorded > > self-reference is not updated appropriately. > > > > In your case a workaround is to call 'self' after all the other updates, > > i.e. > > > > test :: String -> Bool > > test = accept s1 > > where s1 = self '1' . path '0' s2 $ empty True > > s2 = self '1' . path '0' s1 $ empty False > > > > But I don't see why you need 'self' at all -- you can just use path as > > with any other type of transition: > > > > test :: String -> Bool > > test = accept s1 > > where s1 = path '0' s2 . path '1' s1 $ empty True > > s2 = path '0' s1 . path '1' s2 $ empty False > > Indeed this just works, thanks! The reason I was using a 'self' > function was that I initially thought it would be more convenient; I now > see it doesn't, especially considering it doesn't even work. However > I'm a bit confused as to why things just work without having to reorder > the calls when using the 'path' function - my brain seems to have > difficulties following the code path here :-).
Oh, nevermind, I finally figured it out. When using my 'self' function, as you said, I point at the version of the DFA I have when calling 'self', and not the final version of the DFA after other calls to 'path'. So as soon as I was following a self transition, I was ending up with an 'old' version of the DFA. Whereas in your version, the binding I point to is the final DFA version. Thanks a lot! Maxime _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
