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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 was 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)
At least N times	A{N,}	A(N,infinity)
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
Positive lookahead	(?=A)	&A
Negative lookahead	(?!A)	!A
Character	a	text("a")
Any character	.	any()
Character sequence	abc	text("abc")
Character group	[abc]	group("abc")
Character range	[a-z]	range('a', 'z')
Character class	[:alnum:] [:alpha:] ...	alnum() alpha() ...

Examples

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

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

• Match identifier (alphabetic character followed by zero or more alphanumeric characters):

rule digit = range('0', '9');
rule alnum = digit | alpha;
rule identifier1 = alpha >> *alnum; // Alternative #1
rule identifier2 = !digit >> +alnum; // Alternative #2

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

rule floating = -group("+-") >> ( ( *digit >> text(".") >> +digit ) | +digit );