Updated stale imports. Started experiment with parsing system. Got reduction scanner feature ready for use. Added several data utilities.

source/data/iteration-utilities.mjs

@@ -0,0 +1,31 @@
+export class Switchable_Iterator {
+	constructor(iterator=null, stack=[]) {
+		Object.assign(this, { iterator, stack });
+	}
+
+	push(iterator) {
+		this.stack.push(this.iterator);
+		this.switch_to(iterator);
+	}
+
+	pop(iterator) {
+		this.switch_to(this.stack.pop());
+	}
+
+	switch_to(iterator) {
+		this.iterator = iterator;
+	}
+
+	next() {
+		return this.iterator.next();
+	}
+
+	peek() {
+		return this.iterator.peek();
+	}
+
+	[Symbol.iterator]() {
+		return this;
+	}
+
+}

source/data/object-utilities.mjs

@@ -0,0 +1,9 @@
+
+export function assign_defined(target, source) {
+	Object.assign(target, Object.fromEntries(Object.entries(source).filter(([k ,v]) => v !== undefined )));
+}
+
+
+export function assign_using_predicate(target, source, kv_predicate) {
+	Object.assign(target, Object.fromEntries(Object.entries(source).filter(kv_predicate)));	// Call predicate with ([k, v])
+}

source/data/stack.mjs

@@ -0,0 +1,54 @@
+export const DELETE_PROPERTY = Symbol('DELETE_PROPERTY');
+
+
+export class String_Keyed_Stack {
+	constructor(target={}, stack=[]) {
+		Object.assign(this, { target, stack });
+	}
+
+	push(updates={}) {
+		const frame = {}
+		this.stack.push(frame);
+		for (const [key, value] of Object.entries(updates)) {
+
+			if (key in this.target) {
+				frame[key] = this.target[key];
+			} else {
+				frame[key] = DELETE_PROPERTY;
+			}
+
+			if (value === DELETE_PROPERTY) {
+				delete this.target[key];
+			} else {
+				this.target[key] = value;
+			}
+		}
+		return frame;
+	}
+
+	push_defined(updates={}) {
+		this.push(Object.fromEntries(Object.entries(updates).filter(([k ,v]) => v !== undefined )));
+	}
+
+	pop(copy_previous_state=false) {
+		const frame = this.stack.pop();
+		const { target } = this;
+
+		const return_value = copy_previous_state ? { ...target } : null;
+
+		for (const [key, value] of Object.entries(frame)) {
+			if (value === DELETE_PROPERTY) {
+				delete target[key];
+			} else {
+				target[key] = value;
+			}
+		}
+
+		return return_value;
+	}
+
+	get top_reverse_delta() {
+		return this.stack.at(-1);
+	}
+
+}

source/parsing/regexp-dispatch.mjs

@@ -70,12 +70,15 @@ export class Abstract_RegExp_Token_Rule {
 }
 
 export class RegExp_Token_Rule extends Abstract_RegExp_Token_Rule {
-	constructor(pattern, identifier=this) {
+	constructor(pattern, identifier=undefined) {
 		super(pattern);
-		Object.assign(this, { identifier });
+		Object.assign(this, { identifier: identifier ?? this });
 	}
 }
 
+// Note: There is no clean built in way to set an end position of a RegExp pattern, the only generic way is to slice the string we match before.
+//		 We may at some point implement support for this (and it would only be done if end position was given)
+
 export class RegExp_Tokenizer {
 	constructor(rules=[], default_action=undefined) {
 		Object.assign(this, { rules, default_action });