Justin Bailey wrote:
The other day I decided to implement a ring buffer with a current element (i.e. a doubly-linked zipper list).
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p.s. The original motivation for writing this was to model cellular automata. The CA world is "circular", so that got me thinking about a structure that made connecting the ends easy to do.
Note that depending on your concrete setting, you may not need a fancy ring structure for cellular automata. And with simple automata like c'_i = c_(i-1) `xor` c_i `xor` c_(i+1) it may even be easier to generate fresh rings for each step in the automaton: data Context a = Context [a] a [a] -- rotate left rotL (Context ls x (r:rs)) = Context (x:ls) r rs -- description of a cellular automaton type Rule a = Context a -> a example :: Rule Bool example (Context (cm:_) c (cp:_)) = cm `xor` c `xor` cp -- run a cellular automaton on an initial band of cells -- which is considered to be cyclic, i.e. a "cylinder" automate :: Rule a -> [a] -> [[a]] automate f xs = iterate (take n . map f . mkContexts) xs where -- length of the cell band n = length xs mkContexts (x:xs) = iterate rotL $ Context (cycle $ reverse xs) (head xs) (tail $ cycle xs) Here, mkContexts xs initializes a new infinite cyclic "ring" for xs and rotates it left ad infinitum. Regards, apfelmus