Sign in to follow this  

F# Ackermann Stack overflow

This topic is 3495 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

So, I'm tinkering with a memoizing implementation of the Ackermann function using BigInt, and getting a stack overflow. I'm pretty sure I understand why - the closure for the memoization means that it's not able to 'true' tail recursion, so it can't be optimized out to a loop (and, yes, I've tested under Release mode with -O3). Can anyone see how to fix this, or even just comment on style?
#light

open System
open System.Collections.Generic

let memoize f = let cache = new Dictionary<_, _>()
                fun args -> if cache.ContainsKey(args)
                              then cache.[args]
                              else let r = f args
                                   cache.[args] <- r
                                   r

let rec _ack (m, n) = if m = 0I
                        then n + 1I
                        else if n = 0I
                               then ack (m - 1I, 1I)
                               else ack (m - 1I, ack (m, n - 1I))
                            
and ack = memoize _ack
                           
let main = Console.WriteLine(ack (4I, 1I))


Share this post


Link to post
Share on other sites

This topic is 3495 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this