2006/3/15, Paul Johnson <[EMAIL PROTECTED]>: > "minh thu" <[EMAIL PROTECTED]> wrote: > > >2006/3/15, Duncan Coutts <[EMAIL PROTECTED]>: > > > > > >>On Wed, 2006-03-15 at 17:21 +0100, Sebastian Sylvan wrote: > >> > >> > >>>You can also use laziness (untested!): > >>> > >>>data DLink a = (DLink a) a (DLink a) | Nil > >>> > >>>test = d1 > >>> where d1 = Nil 5 d2 > >>> d2 = d1 6 Nil > >>> > >>>test here is a linked list containing 5 and the next node containing > >>>6. Both nodes have references to the next and previous links (wich is > >>>Nil at the ends). The magic here is laziness. You reference d2 in the > >>>definition for d1 and d1 in the definition for d2. It gets sort of > >>>clumsy to work with, though. You're probably better off using STRefs > >>>(for example) if you really need that type of data structures... > >>> > >>> > >>I wrote a talk once on this topic: > >>http://web.comlab.ox.ac.uk/oucl/work/duncan.coutts/papers/recursive_data_structures_in_haskell.pdf > >> > >>Duncan > >> > >> > >thanks, but I cannot construct the whole sturcture in one time (i need > >incremental update). > > > > > You might also go back and think about why you needed that double linked > list in the first place. Many things that require complicated list > structures in C are better represented as compositions of functions. > The simplest example is StringS in the Standard Prelude, which avoids > O(n^2) behaviour in list concatenation by composing functions instead. > Similarly you might find that by representing your data structure as the > composition of the functions needed to build it you can defer creation > of the actual structure to the point at which it gets read. Then all > the closures get evaluated, but the evaluated stuff stays around and > acts as the foundation for subsequent updates. It all depends on what > you want to do. > hi, to be clear, the data structure i'm thinking of is the "half edge" or "winged edge" : data structures to represent a 3d mesh in 3d modeling apps (thus, a constraint is that it can handle lot of data and fast updates).
the idea of creating the data structure in plain c (and maybe the basic functions) and then use it (them) in haskell is bad ? thanks, vo minh thu _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
