Misleading resource name

[UWN]

(according to git blame, this is from 2024-05-13 18:00:56 in src/machine/machine_errors.rs. So it is unrelated to the recent progress. That is, thanks to recent progress, this error is now uncovered as seen below)

?- length(_,E),N is 2^2^E, catch(( length(L,N), length(L,M) ), Error,true).
   E = 0, N = 2, L = [_A,_B], M = 2
;  E = 1, N = 4, L = [_A,_B,_C,_D], M = 4
;  E = 2, N = 16, L = [_A,_B,_C,_D,_E,_F,_G,_H,_I,_J,_K,_L,_M,_N,_O,_P], M = 16
;  E = 3, N = 256, L = [_A,_B,_C,_D,_E,_F,_G,_H,_I,_J,_K,_L,_M,_N,_O,_P,_Q,_R,_S,_T|...], M = 256
;  E = 4, N = 65536, L = [_A,_B,_C,_D,_E,_F,_G,_H,_I,_J,_K,_L,_M,_N,_O,_P,_Q,_R,_S,_T|...], M = 65536
;  E = 5, N = 4294967296, Error = error(resource_error(memory),[]) % new & nice
;  E = 6, N = 18446744073709551616, Error = error(resource_error(finite_memory,18446744073709551616),length/2), unexpected.
;  ... .

Unexpected is the resource name finite_memory. This name has been used so far for cases where only an infinite amount of memory would solve the problem. But here, we have 2^2^6 which is a very finite number. Maybe big compared to the (current) address space, but still very finite. So a (much) bigger memory would solve the problem.

[Skgland]

I think you are talking about these lines

scryer-prolog/src/machine/machine_errors.rs

Lines 333 to 338 in f570e56

	ResourceError::FiniteMemory(size_requested) => {
	functor!(
	atom!("resource_error"),
	[atom_as_cell((atom!("finite_memory"))), cell(size_requested)]
	)
	}

It looks like the only place that emits this error is

scryer-prolog/src/machine/system_calls.rs

Lines 4379 to 4386 in f570e56

	Ok(Number::Integer(n)) => match (&*n).try_into() as Result<usize, _> {
	Ok(n) => n,
	Err(_) => {
	let err = MachineState::resource_error(ResourceError::FiniteMemory(len));
	return Err(self.machine_st.error_form(err, stub_gen()));
	}
	},
	_ => {

So we failed to convert the number in heap cell len to usize,
given that allocations need to fit in isize::MAX (which is less than usize::MAX) this allocation would exceede the maximum allocation size of the architecture scryer-prolog is compiled for.

While technical still a finite size it is larger than the than the maximum size possible (on the current architectur) not just the maximum size available (on this machines current configuration).

[UWN]

In some situations (not this one), a representation error would be appropriate to express the architectural limitation. But not here.

[UWN]

There is also the other problem: The term should be resource_error(memory) alone, but there is this additional second argument which should not be there.

[UWN]

(Solved with #3207)