[Haskell-cafe] Criteria for determining if a recursive function can be implemented in constant memory

[Andrew Coppin]

Tillmann Rendel wrote:
> Hi Steffen,
>
> Steffen Schuldenzucker wrote:
>> Given the definition of a recursive function f in, say, haskell, 
>> determine if f can be implemented in O(1) memory.
>
> Constant functions are implementable in O(1) memory, but interpreters 
> for turing-complete languages are not, so the property of being 
> implementable in O(1) memory is non-trivial and therefore, by Rice's 
> theorem, undecidable.

Damn Rice's theorum, spoiling everybody's fun all the time... ;-)

Of course, as I understand it, all the theorum says is that no single 
algorithm can give you a yes/no answer for *every* possible case. So the 
next question is "is it decidable in any 'interesting' cases?"

Then of course you have to go define 'interesting'...