[Haskell-beginners] Circular Linked Lists
bayer at cpw.math.columbia.edu
Tue Feb 3 08:56:34 EST 2009
On Feb 2, 2009, at 9:45 PM, Matthew J. Williams wrote:
> Dear All
> How would one mimic, in Haskell, a C++ circular linked list i.e.,
> where the last element precedes (points to) the first?
You are getting deep answers to what is perhaps a simple question. You
haven't said exactly what you want to do with a circular linked list,
and people are perhaps fearing the trickiest applications.
Have you tried the Prelude function cycle?
> cycle :: [a] -> [a]
> cycle ties a finite list into a circular one, or equivalently, the
> infinite repetition of the original list. It is the identity on
> infinite lists.
For instance, in ghci one gets
> Prelude> [1..3]
> Prelude> take 10 $ cycle [1..3]
cycle doesn't actually construct in memory a cyclic data structure, as
one might in C. It's more like those repeat bars in sheet music.
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