On Wed, 2006-03-15 at 17:21 +0100, Sebastian Sylvan wrote: > On 3/15/06, minh thu <[EMAIL PROTECTED]> wrote: > > hi everybody, > > > > i have to implement some data structure which is usually implemented > > with pointers in imperative languages (can think of it as a double > > linked list). > > > > i'd like to know how i have to do that. > > > > is there any standard way of converting pointer-based data structure > > into an inductively-defined data type (like standard haskell list) ? > > is-it possible ? > > > > or would it be good to define the data structure in c and write a > > haskell wrapper around the c code ? > > > > thank you a lot, bye, > > vo minh thu > > You can use references, IO, ST or STM. > > 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 _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
