`get_args`, and drop `Node`

[arvidn]

This change moves away from Node as the abstraction to iterate over lists, replacing it with two lower level facilities:

• Allocator::next() - a function that can be used in while conditions to loop over a list.
• get_args() and get_varargs() - functions that match and extracts arguments from argument lists. This replaces the need for checking the number of arguments as well as picking out the nodes by iterating or calling first()?.node.

Some utility functions (in op_utils.rs) were changed to take an &Allocator + NodePtr rather than &Node as well, to allow dropping the Node class.

The get_args() abstraction is a quite nice improvement to the ergonomics of the operator implementations, and in my mind is the main motiviation for this patch.

I added a few missing unit tests for the updated utility functions as well as Allocator::atom_len().

The original intention of removing the Node abstraction was to allow for Allocator references to be mutable, and have Allocator::atom() (and related functions) take a mutable reference to the allocator. However, some experimentation beyond this point suggests that's actually impractical. But I think this step is still an improvement.

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 5294089619

• 433 of 442 (97.96%) changed or added relevant lines in 7 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.08%) to 92.995%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/run_program.rs	22	23	95.65%
src/more_ops.rs	100	108	92.59%
<!--	Total:	433	442	97.96%	-->

Files with Coverage Reduction	New Missed Lines	%
src/run_program.rs	1	97.52%
<!--	Total:	1		-->

Totals
Change from base Build 5294056862:	0.08%
Covered Lines:	5138
Relevant Lines:	5525

---

💛 - Coveralls

[arvidn]

I'll address these comments in a separate PR. I hope that's OK.

This message isn't quite right. The idea it's trying to get across is that X must be an atom and not a cons. It can take multiple arguments (which are implicitly quoted).

Yeah, I agree that I was a bit lazy in making that use of get_args() produce a good error message. I'd prefer to keep get_args() relatively simple, and not make the error message it produces configurable (because it's good in almost all cases). I could make it say: in the ((X)...) syntax, the inner list takes exactly 1 argument

This might work (and cargo fmt will clean it up better):

string literals don't automatically concatenate in rust, but you can insert line breaks using \.

((+) 1 2 3) = 6 We should make sure there is at least one test of this.

There is at least one positive test for this construct, I'll add this example as well.

[arvidn]

https://github.com/Chia-Network/clvm_rs/pull/316