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BNFA is C++ regular expression matcher based on non-deterministic finite automata (NFA).

Rules

BNFA uses overloaded operators for writing regular expressions. This syntax has been inspired by Boost.Spirit (www.boost.org).

Element	Regular expression	BNFA
Optional	a?	-a
One-or-more	a+	+a
Zero-or-more	a*	*a
Exactly n times	a{n}	a(n)
Between m and n times	a{m,n}	a(m,n)
Concatenation	ab	a >> b
Alternation	a | b	a | b
Separated list	a(ba)*	a % b
Character	a	text("a")
Any character	.	any()
Character sequence	abc	text("abc")
Character group	[abc]	group("abc")
Character range	[a-z]	range('a', 'z')
Positive lookahead	(?=a)	&a
Negative lookahead	(?!a)	!a

Examples

• Match alphabetic letters with [A-Za-z]:

rule alphabetic = range('A', 'Z') | range('a', 'z');

• Matching a floating point number can be done with the regular expression [+-]?([0-9]*\.[0-9]+|[0-9]+):

rule digit = range('0', '9');
rule floating = -( group("+-") ) >> ( ( *digit >> text(".") >> +digit ) | +digit );