[R] Continuation-parsing / trampoline / infinite recursion problem

Thomas Mailund
Wed, 10 Aug 2016 17:17:05 -0000

But wait, how is it actually changing? And how did calling `cat` make the
problem go away?

Ok, I will go think about it?

Thanks anyway, it seems to do the trick.


> On 10 Aug 2016, at 19:10, Thomas Mailund <mailund at birc.au.dk>
wrote:
>
>
> That did the trick!
>
> I was so focused on not evaluating the continuation that I completely
forgot that the thunk could hold an unevaluated value? now it seems to be
working for all the various implementations I have been playing around with.
>
> I think I still need to wrap my head around *why* the forced evaluation is
necessary there, but I will figure that out when my tired brain has had a little
rest.
>
> Thanks a lot!
>
> 	Thomas
>
>
>> On 10 Aug 2016, at 19:04, Duncan Murdoch <murdoch.duncan at
gmail.com> wrote:
>>
>> On 10/08/2016 12:53 PM, Thomas Mailund wrote:
>>>> On 10 Aug 2016, at 13:56, Thomas Mailund <mailund at
birc.au.dk> wrote:
>>>>
>>>> make_thunk <- function(f, ...) f(...)
>>>
>>> Doh!  It is of course this one:
>>>
>>> make_thunk <- function(f, ...) function() f(?)
>>>
>>> It just binds a function call into a thunk so I can delay its
evaluation.
>>
>> I haven't looked closely at the full set of functions, but this
comment:
>>
>> force(continuation) # if I remove this line I get an error
>>
>> makes it sound as though you're being caught by lazy evaluation.
The "make_thunk" doesn't appear to evaluate ..., so its value can
change between the time you make the thunk and the time you evaluate it.  I
think you could force the evaluation within make_thunk by changing it to
>>
>> make_thunk <- function(f, ...) { list(...); function() f(?) }
>>
>> and then would be able to skip the force() in your thunk_factorial
function.
>>
>> Duncan Murdoch
>>
>>
>
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