feat(api/iota): endofunctors

[poolcritter]

adds visit and visitChildren to iotas letting you apply a UnaryOperator to an entire tree of them. this is like hexal's IMappableIota except I don't know if that does self pre or post (or if it does self at all). awa.

I haven't tested this in prod; hex doesn't have anything that would use this yet. @IridescentVoid I believe you have a patch that may want to use this?

Cc: @IridescentVoid
Change-Id: Ic464f4702ba9b0379c93e31723e2a5fe6a6a6964
Issue: closes #1083

[IridescentVoid]

github ate the comment I left on the file. see review below instead.

[IridescentVoid]

Code-Review: -1

Implementation of visitChildren should be made more readable. I would like to at least see full-length variable names.

I'd also like feedback from others on the API design since changing this later would be a breaking change.

[IridescentVoid]

This section is pretty hard to read. I would suggest the following snippet instead, which should be equivalent. Changes I've made:

• Gave variables longer names.
• Use explicit types instead of var for slightly better readability. (IMHO, SpellList being written directly is better.)
• Change the array to an ArrayList as SpellList.size() is O(n). This also eliminates a piece of state that needs tracking, the index, which helps with code understanding.
• Reordered some statements to follow what seemed to me as the most logical order.

Suggested change

	var o = new Iota[getList().size()];
	int w = 0;
	boolean k = true;
	var p = getList();
	while (p.getNonEmpty()) {
	var r = visitor.apply(p.getCar());
	k &= r == p.getCar();
	o[w++] = r;
	p = p.getCdr();
	}
	return k ? this : new ListIota(Arrays.asList(o));
	SpellList ptr = getList();
	ArrayList<Iota> updatedChildren = new ArrayList<>();
	boolean modified = false;
	while (ptr.getNonEmpty()) {
	var newChild = visitor.apply(ptr.getCar());
	updatedChildren.add(newChild);
	modified = modified || newChild != ptr.getCar();
	ptr = ptr.getCdr();
	}
	return !modified ? this : new ListIota(updatedChildren);