Taken at face-value, it would certainly seem like RAII works against TCO. However, remember that there are a number of ways in which the compiler can “get away with it”, so to speak. The first and most obvious case is if the destructor is trivial, meaning that it is the default destructor (compiler-generated) and all … Read more
You should definitely check out http://research.microsoft.com/en-us/um/cambridge/projects/fsharp/manual/FSharp.PowerPack/Microsoft.FSharp.Collections.LazyList.html but I will try to post a more comprehensive answer later. UPDATE Ok, a solution is below. It represents the Morris sequence as a LazyList of LazyLists of int, since I presume you want it to be lazy in ‘both directions’. The F# LazyList (in the FSharp.PowerPack.dll) has three … Read more
Tail Calls If a function call is a last action performed in another function, it is said to be a tail call. The name stems from the fact that the function call appears at the tail position of other function. int foo(int a, int b) { // some code … return bar(b); // Tail call … Read more
As always, continuations yield an elegant tailcall solution: open System.Collections.Generic let cache = Dictionary<_,_>() // TODO move inside let memoizedTRFactorial = let rec fac n k = // must make tailcalls to k match cache.TryGetValue(n) with | true, r -> k r | _ -> if n=0 then k 1 else fac (n-1) (fun r1 … Read more
The tail position is a position which an expression would return a value from. There are no more forms evaluated after the form in the tail position is evaluated. Consider this example from The Joy of Clojure (defn absolute-value [x] (if (pos? x) x ; “then” clause (- x))) ; “else” clause It takes a … Read more
Statements like “C doesn’t perform tail call elimination” make no sense. As you correctly noted yourself, things like this depend entirely on the implementation. And yes, any decent implementation can easily turn tail-recursion into [an equivalent of] a cycle. Of course, C compilers do not normally give any guarantees about what optimizations will and what … Read more
Test results (after reducing array size to 20000000) Under Java 1.6.22 I get 151 and 122 ms for tail-recursion and while-loop respectively. Under Java 1.7.0 I get 55 and 101 ms So under Java 6 your while-loop is actually faster; both have improved in performance under Java 7, but the tail-recursive version has overtaken the … Read more
C# does not innately support tail recursion in the language but here is an interesting article on a similar technique call trampolining that may help you in your situation
Tail call elimination is an optimization that saves stack space. It replaces a function call with a goto. Tail recursion elimination is the same thing, but with the added constraint that the function is calling itself. Basically, if the very last thing a function A does is return A(params…) then you can eliminate the allocation … Read more