GerHobbelt

Note: I'm not native English speaking and don't have the natural language processing jargon down pat, so the 'preceeding' vs. 'proceeding' I assume the PREceeding text before 'x' in 'zzxz' is the leading 'zz' ('history') and the PROceeding text for the same is the trailing 'z', hence 'proceeding text' would be similar to 'look ahead' as it is called in computer language parsing (unambiguous language parsing).

Anyway... I'm sure I don't get everything you say but there's at least one subject which is certainly relevant here:

handling/coping with history (preceeding input) vs. look-ahead (future, incoming, proceeding input)

In your sample grammar and sample 'zzxz' I assume each character is a single token. (Yes, PEG always processes characters as it blends lexer and parser into a single specification language; I'm just sufficiently dinosaur to appreciate the difference between 'character stream' and 'token stream': the token stream is where such nice horrors as left recursion are to be ex

GerHobbelt

xxx

GerHobbelt

This code is a stripped version of actual production code which employs this JISON clone:

(https://github.com/GerHobbelt/jison)

hence make sure to diff that one against vanilla to see differences/features.

---

code shows .yy.parseError, lexer.post_lex, parser.post_parser, how to get the token identifier strings from the JISON-generated parser class, etc.

GerHobbelt

// Use Gists to store code you would like to remember later on
console.log(window); // log the "window" object to the console

GerHobbelt

%options ranges
%options backtrack_lexer

/*
 * lexical grammar
 * ===============
 *
 * This section defines the lexer rules for our formula parser. The rules are checked from top to bottom, so order is import
 * here!
 *

GerHobbelt

Intent

Collection of references ('from a time when graphic skills did not mean hitting the Print button on an Excel Chart')

Origins

Scans originate from some classic books, owned by yours truly:

GerHobbelt

*.sh            text eol=lf
*.php           text eol=lf
*.inc           text eol=lf
*.html          text eol=lf
*.js            text eol=lf
*.css           text eol=lf
*.ini           text eol=lf
*.txt           text eol=lf
*.xml           text eol=lf
*.md            text eol=lf

GerHobbelt

Basic Compiler Technology

Lexers, Parsers, Code Generators are of all ages (old skool: lex/flex, yacc/bison (modern-ish: PCCTS/ANTLR), burg/lburg/...)

Here's an example of a JavaScript based domain-specific language being parsed and converted into HTML. It is very similar to wiki and MarkDown formats; the only purpose of this code is to showcase the parsing technology, so a minimum number of 'shortcuts' and other production code 'smartness' is applied.

The recursive descent parser works by evaluating the grammar rules in order of precedence, where each function call is a grammar rule match attempt and the first one returning success is a 'grammar rule match' which will allow the parser to continue parsing the input.

Also, the input is assumed to be size limited, i.e. a infinite lookahead grammar is fine with us. (This doesn't work in situations where you need to parse a stream, but that is a problem area that few of us have to deal with in actual reality. Mostly we like limited lookahead grammars becaus

GerHobbelt

{
  "tip_of_the_day": [
    {
		"title": "Introduction",
		"description": [
			"A huge image is shown on screen; you can pan/zoom the image to see all the detail or the entire image at once.",
			"Each of the possible operations can be performed by one of several mouse actions, some operations can also be performed using the keyboard."
		]
	},
    {

GerHobbelt

Here's a d3 plugin that allows you to create a polygon selection. You instantiate it just like d3.svg.brush.

var brush = d3.svg.polybrush();

It has an extra public method that 'brush' does not, and that's 'isWithinExtent(x, y)'. You can use this method to test if a given point falls within the drawn extent.

if (brush.isWithinExtent(x, y)) {
  console.log("I'm inside!");
}