Dmitry Soshnikov DmitrySoshnikov

@kangax's ES6 quiz, explained

@kangax created a new interesting quiz, this time devoted to ES6 (aka ES2015). I found this quiz very interesting and quite hard (made myself 3 mistakes on first pass).

Here we go with the explanations:

Question 1:

(function(x, f = () =&gt; x) {

"Shift-reduce" and "Reduce-reduce" conflicts in LR parsing.

How to determine?

A full parsing table is not needed, only the canonical collection. In the canonical collection, find all final items (and only final items), and see if:

There are both shift and reduce in the same item ("shift-reduce", s/r)
There are two reduce actions in the same item ("reduce-reduce", r/r)

If none of these is true, there are no conflicts, even in LR(0). If there are some of the above, SLR(1) still may solve it.

	/**
	* Cooperative tasks scheduler.
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style License
	*
	* An educational implementation to show the work of a processes scheduler.
	* In practice you may find using a library like Task.js, or similar.
	*
	* Test, Node 4 or transformed with Babel:

	/**
	* Depth-first and Breadth-first graph traversals.
	*
	* In this diff we implement non-recursive algorithms for DFS,
	* and BFS maintaining an explicit stack and a queue.
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style license
	*/

	/**
	* LR-parsing.
	*
	* Canonical collection of LR(0) items.
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style License (C) 2015
	*
	* See this "rock-painting" to get the picture of what we're building here:
	*

	{
	"lex": {
	"macros": {
	"digit": "[0-9]",
	"esc": "\\\\",
	"int": "-?(?:[0-9]\|[1-9][0-9]+)",
	"exp": "(?:[eE][-+]?[0-9]+)",
	"frac": "(?:\\.[0-9]+)"
	},
	"rules": [

	%token STRING NULL NUMBER TRUE FALSE

	%start JSONText

	%%

	JSONText : JSONValue;

	JSONString : STRING;

	/**
	* Destructuring reference bindings.
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style License
	*/

	// Bindings of a pattern in destructuring may be not only
	// simple variables, but any reference types. In the following
	// example we use destructuring assignment to swap two elements

	###
	# Explicit delegation-based prototypes implementation.
	#
	# Implementing JavaScript semantics.
	#
	# Here we show that "delegation" is just a mechanism (a pattern) for
	# implementation of the "inheritance" concept. In this specific case we
	# have direct inheritance from objects, skipping the "class" step.
	#
	# See "OO Relationships" article for some details:

	/**
	* "Is connected?"
	*
	* Dynamic connectivity issue.
	*
	* 1 2: not connected
	* 1--2: connected
	* 1--2--3: 1 and 3 are connected through 2
	*
	* This implementation uses concept of a "weight" to avoid too long trees: