Dmitry Soshnikov DmitrySoshnikov

"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.

@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) {

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

	/**
	* 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:
	*

	/**
	* 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
	*/

	/**
	* 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:

	# Compiled code sharing between
	# several functions.

	arr = []
	for k in [1, 2, 3]:
	arr.append(lambda: k)

	print(arr[0].__code__ == arr[1].__code__) # True
	print(arr[0].__code__.co_code) # bytecode

	# Python
	#
	# Closures when they are used as default params, capture bindings
	# from the environment one level above the class.
	#

	x = 1 # global env

	def wrap():

	/**
	* Building LL(1) parsing table from First and Follow sets.
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style License
	*
	* This diff is a continuation of what we started in the previous two diffs:
	*
	* Dependencies:
	*

	/**
	* LL(1) parser. Building parsing table, part 1: First and Follow sets.
	*
	* NOTICE: see full implementation in the Syntax tool, here:
	* https://github.com/DmitrySoshnikov/syntax/blob/master/src/sets-generator.js
	*
	* by Dmitry Soshnikov <[email protected]>
	* MIT Style License
	*
	* An LL(1)-parser is a top-down, fast predictive non-recursive parser,