Oh, I see that the make_thunk function is missing in my example. It is just this one
make_thunk <- function(f, ...) f(...) On 9 August 2016 at 21:57:05, Thomas Mailund (mail...@birc.au.dk(mailto:mail...@birc.au.dk)) wrote: > [I’m really sorry if you receive this mail twice. I just noticed I had sent > it from a different account that the one I signed up to the mailing list on > and I don’t know if that means it will be filtered; at least I haven’t > received it myself yet.] > > > I am playing around with continuation-passing style recursions and want to > use the trampoline approach to avoiding too deep recursions. I want to do > recursions on a tree so I cannot simply simulate a tail-recursion with a loop > and need something else, and rather than simulating my own stack I want to > use the method that solves this in general. > > I cannot seem to get out of problems with the > > Error: evaluation nested too deeply: infinite recursion / > options(expressions=)? > Error during wrapup: evaluation nested too deeply: infinite recursion / > options(expressions=)? > > error, so I reduced the problem to just computing factorials to see if I > could at least get it to work there, but here I get the problem as well, and > in the example below I am completely stumped as to why. > > trampoline <- function(thunk) { > while (is.function(thunk)) thunk <- thunk() > thunk > } > > thunk_factorial <- function(n, continuation = identity, acc = 1) { > force(continuation) # if I remove this line I get an error > cat("call: ", n, " : ", acc, "\n") # same for this line > if (n == 1) { > continuation(acc) > } else { > make_thunk(thunk_factorial, n - 1, continuation, n * acc) > } > } > trampoline(thunk_factorial(10000)) > > This version works for me. If I remove the “force(continuation)” it doesn’t — > even though I never modify the contination in this function (in the tree I > want to do recursion on I will have to). I get all the way down the simulated > recursion to the final call of the continuation and then I get the error. So > as far as I would expect I should just get the identity of the final > accumulator at the end, but instead I get the error. > > If I remove the cat-call I also get the error. That *really* puzzles me. What > is cat doing that lets me complete the function when it is involved but not > when I comment out that line? > > There is clearly something about this infinite recursion error I am > completely missing. Any help would be greatly appreciated. > > Cheers > Thomas > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
