pegger

Introduction

Base Usage

Rules

Rule	Definition	PEG	EBNF
String	p.string('match_me')	"match_me" 'match_me'	"match_me"
Character class	p.char('a', 'z') p.char('0', '9')	[a-z] [0-9]	"a" | "b" | ... | "z" "0" | "1" | ... | "9"
Any	p.any()	.
Optional	p.opt(rule)	rule?	[rule]
Zero-or-more	p.zeroPlus(rule)	rule*	{rule}
One-or-more	p.onePlus(rule)	rule+	rule, {rule}
Pos. Lookahead	p.and(rule)	&rule
Neg. Lookahead	p.not(rule)	!rule
Sequence	p.seq([first, second])	first second	first, second
Choice	p.choice([first, second])	first | second	first | second

The Grammar

Goals

• Implement original PEG Form
• Implement EBNF Form
• Implement McKeeman Form

Non-Context-Free Languages

Some non-context-sensitive languages can be parsed by PEG. Take the language

$$ {a^n b^n c^n | n \in \mathbb{N}_1 } $$

All strings of this language can be matched by a grammar with the following definition:

S := &(A 'c') 'a'+ B !.
A := 'a' A? 'b'
B := 'b' B? 'c'