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copied!<p>Here's something that's almost a direct translation of the same solution strategy.</p> <p>That said, I think there may be a better/simpler representation choice, I'm still mulling it over.</p> <pre><code>type Runner = int -> Result and Result = Result of int * option<Runner> let AddOne = fun x -> Result(x+1, None) let Idle = fun x -> Result(x, None) let rec Pair(r1,r2) = fun x -> match r1 x with | Result(data,None) -> Result(data, Some(r2)) | Result(data,Some(next)) -> Result(data,Some(Pair(next,r2))) let rec Repeat r n = fun x -> if n = 0 then r x else match r x with | Result(data,None) -> Result(data, Some(Repeat r (n-1))) | Result(data,Some(next)) -> Result(data, Some(Pair(next, Repeat r (n-1)))) </code></pre> <p>EDIT</p> <p>Here's another way that's a little more refined... am still trying to see if there's a good way to work in a "list", since the results seem isomorphic to cons cells...</p> <pre><code>type Runner = Runner of (int -> int * option<Runner>) let AddOne = Runner(fun x -> x+1, None) let Idle = Runner(fun x -> x, None) let rec Pair(Runner(r1),R2) = Runner(fun x -> match r1 x with | data,None -> data, Some(R2) | data,Some(next) -> data, Some(Pair(next,R2))) let rec Repeat (Runner(r) as R) n = Runner(fun x -> if n = 0 then r x else match r x with | data,None -> data, Some(Repeat R (n-1)) | data,Some(next) -> data, Some(Pair(next, Repeat R (n-1)))) </code></pre> <p>EDIT</p> <p>One more version, it uses lists, but now I've a feeling for what's weird here...</p> <pre><code>type Runner = Runner of (int -> int * list<Runner>) let AddOne = Runner(fun x -> x+1, []) let Idle = Runner(fun x -> x, []) let rec Pair(Runner(r1),R2) = Runner(fun x -> match r1 x with | data,xs -> data, xs @ [R2]) // inefficient let rec Repeat (Runner(r) as R) n = Runner(fun x -> if n = 0 then r x else match r x with | data,xs -> data, xs @ List.init (n-1) (fun _ -> R)) // inefficient </code></pre> <p>It's almost just like an 'Action queue', a list of <code>int->int</code> functions. But each guy can produce some 'suffix actions' that run immediately after him (but before the remaining work in the would-be queue), and trying to maintain the ordering with a purely functional data structure is potentially inefficient (without the right tree/queue library at hand). It would be interesting to know how this will be used/consumed, as perhaps a small change there might allow for a completely different strategy.</p>

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