grammar FilterLexer
	# Complex combinations

	rule expression
		space? (expression_compound / body) space? <Expression>
	end

	rule expression_compound
		body space? combine_operator space? expression <Expression>
	end

	rule body
		group / filter
	end

	rule group
		'(' expression ')' <Group>
	end

	# Filters

	rule filter 
		filter_equality / filter_comparison / filter_like
	end

	rule filter_equality
		identifier space? equality_operator space? value <Filter>
	end

	rule filter_comparison
		identifier space? comparison_operator space? number <Filter>
	end

	rule filter_like
		identifier space like_operator space string <Filter>
	end

	# Logic

	rule combine_operator
		or_operator / and_operator
	end

	rule or_operator
		'' ('||' / 'OR' / 'or') <OrOperator>
	end

	rule and_operator
		'' ('&&' / 'AND' / 'and') <AndOperator>
	end

	# Operators

	rule equality_operator
		eq_operator / neq_operator
	end

	rule comparison_operator
		le_operator / lt_operator / ge_operator / gt_operator
	end

	rule like_operator
		yes_like_operator / not_like_operator
	end

	rule eq_operator
		'==' <EQOperator>
	end

	rule neq_operator
		'' ('!=' / '<>') <NEQOperator>
	end

	rule lt_operator
		'<' <LTOperator>
	end

	rule le_operator
		'<=' <LEOperator>
	end

	rule gt_operator
		'>' <GTOperator>
	end

	rule ge_operator
		'>=' <GEOperator>
	end

	rule yes_like_operator
		'' ('like' / 'LIKE' / '~=') <LikeOperator>
	end

	rule not_like_operator
		'' ('!~=' / 'NOT LIKE' / 'not like') <NotLikeOperator>
	end

	# Literals

	rule value
		value_special / number / string
	end

	rule value_special
		null / boolean 
	end

	rule number
		number_sign? (number_float / number_integer) number_exponent? <NumberLiteral>
	end

	rule number_integer
		number_base
	end

	rule number_float
		number_base '.' number_base
	end

	rule number_sign
		'+' / '-'
	end

	rule number_exponent
		'e' number_base
	end

	rule number_base
		[0-9]+
	end

	rule boolean
		boolean_true / boolean_false
	end

	rule boolean_true
		'' ('true' / 'TRUE' / 'on' / 'ON' / 'yes' / 'YES') <BooleanLiteralTrue>
	end

	rule boolean_false
		'' ('false' / 'FALSE' / 'off' / 'OFF' / 'no' / 'NO') <BooleanLiteralFalse>
	end

	rule null
		'' ('null' / 'NULL' / 'nil' / 'NIL' / 'nul' / 'NUL') <NullLiteral>
	end

	rule string
		string_single / string_double
	end

	rule string_single
		"'" ([^'\\] / "\\" . )* "'" <StringLiteral>
	end

	rule string_double
		'"' ([^"\\] / "\\" . )* '"' <StringLiteral>
	end

	rule identifier
		[a-zA-Z] [a-zA-Z0-9_]* <Identifier>
	end

	# Whitespace

	rule space
		[\s]+
	end
end