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native.rb
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native.rb
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module EBNF
module Native
##
# Native parser for EBNF; less accurate, but appropriate when changing EBNF grammar, itself.
#
# Iterate over rule strings.
# a line that starts with '\[' or '@' starts a new rule
#
# @param [StringScanner] scanner
# @yield rule_string
# @yieldparam [String] rule_string
def eachRule(scanner)
cur_lineno = 1
r = ''
until scanner.eos?
case
when s = scanner.scan(%r(\s+)m)
# Eat whitespace
cur_lineno += s.count("\n")
#debug("eachRule(ws)") { "[#{cur_lineno}] #{s.inspect}" }
when s = scanner.scan(%r(/\*([^\*]|\*[^\/])*\*/)m)
# Eat comments /* .. */
cur_lineno += s.count("\n")
debug("eachRule(comment)") { "[#{cur_lineno}] #{s.inspect}" }
when s = scanner.scan(%r(\(\*([^\*]|\*[^\)])*\*\))m)
# Eat comments (* .. *)
cur_lineno += s.count("\n")
debug("eachRule(comment)") { "[#{cur_lineno}] #{s.inspect}" }
when s = scanner.scan(%r((#(?!x)|//).*$))
# Eat comments // & #
cur_lineno += s.count("\n")
debug("eachRule(comment)") { "[#{cur_lineno}] #{s.inspect}" }
when s = scanner.scan(/\A["']/)
# Found a quote, scan until end of matching quote
s += scanner.scan_until(/#{scanner.matched}|$/)
r += s
when s = scanner.scan(%r(^@terminals))
#debug("eachRule(@terminals)") { "[#{cur_lineno}] #{s.inspect}" }
yield(r) unless r.empty?
@lineno = cur_lineno
yield(s)
r = ''
when s = scanner.scan(/@pass/)
# Found rule start, if we've already collected a rule, yield it
#debug("eachRule(@pass)") { "[#{cur_lineno}] #{s.inspect}" }
yield r unless r.empty?
@lineno = cur_lineno
r = s
when s = scanner.scan(EBNF::Terminals::LHS)
# Found rule start, if we've already collected a rule, yield it
yield r unless r.empty?
#debug("eachRule(rule)") { "[#{cur_lineno}] #{s.inspect}" }
@lineno = cur_lineno
r = s
else
# Collect until end of line, or start of comment or quote
s = scanner.scan_until(%r{(?:[/\(]\*)|#(?!x)|//|["']|$})
if scanner.matched.length > 0
# Back up scan head before ending match
scanner.pos = scanner.pos - scanner.matched.length
# Remove matched from end of string
s = s[0..-(scanner.matched.length+1)]
end
cur_lineno += s.count("\n")
#debug("eachRule(rest)") { "[#{cur_lineno}] #{s.inspect}" }
r += s
end
end
yield r unless r.empty?
end
##
# Parse a rule into an optional rule number, a symbol and an expression
#
# @param [String] rule
# @return [Rule]
def ruleParts(rule)
num_sym, expr = rule.split('::=', 2).map(&:strip)
num, sym = num_sym.split(']', 2).map(&:strip)
num, sym = "", num if sym.nil?
num = num[1..-1]
r = Rule.new(sym && sym.to_sym, num, expression(expr).first, ebnf: self)
debug("ruleParts") { r.inspect }
r
end
##
# Parse a string into an expression tree and a remaining string
#
# @example
# >>> expression("a b c")
# ((seq a b c) '')
#
# >>> expression("a? b+ c*")
# ((seq (opt a) (plus b) (star c)) '')
#
# >>> expression(" | x xlist")
# ((alt (seq) (seq x xlist)) '')
#
# >>> expression("a | (b - c)")
# ((alt a (diff b c)) '')
#
# >>> expression("a b | c d")
# ((alt (seq a b) (seq c d)) '')
#
# >>> expression("a | b | c")
# ((alt a b c) '')
#
# >>> expression("a) b c")
# (a ' b c')
#
# >>> expression("BaseDecl? PrefixDecl*")
# ((seq (opt BaseDecl) (star PrefixDecl)) '')
#
# >>> expression("NCCHAR1 | diff | [0-9] | #x00B7 | [#x0300-#x036F] | \[#x203F-#x2040\]")
# ((alt NCCHAR1 diff
# (range '0-9')
# (hex '#x00B7')
# (range '#x0300-#x036F')
# (range, '#x203F-#x2040')) '')
#
# @param [String] s
# @return [Array]
def expression(s)
debug("expression") {"(#{s.inspect})"}
e, s = depth {alt(s)}
debug {"=> alt returned #{[e, s].inspect}"}
unless s.to_s.empty?
t, ss = depth {terminal(s)}
debug {"=> terminal returned #{[t, ss].inspect}"}
return [e, ss] if t.is_a?(Array) && t.first == :")"
end
[e, s]
end
##
# Parse alt
# >>> alt("a | b | c")
# ((alt a b c) '')
# @param [String] s
# @return [Array]
def alt(s)
debug("alt") {"(#{s.inspect})"}
args = []
while !s.to_s.empty?
e, s = depth {seq(s)}
debug {"=> seq returned #{[e, s].inspect}"}
if e.to_s.empty?
break unless args.empty?
e = [:seq, []] # empty sequence
end
args << e
unless s.to_s.empty?
t, ss = depth {terminal(s)}
break unless t[0] == :alt
s = ss
end
end
args.length > 1 ? [args.unshift(:alt), s] : [e, s]
end
##
# parse seq
#
# >>> seq("a b c")
# ((seq a b c) '')
#
# >>> seq("a b? c")
# ((seq a (opt b) c) '')
def seq(s)
debug("seq") {"(#{s.inspect})"}
args = []
while !s.to_s.empty?
e, ss = depth {diff(s)}
debug {"=> diff returned #{[e, ss].inspect}"}
unless e.to_s.empty?
args << e
s = ss
else
break;
end
end
if args.length > 1
[args.unshift(:seq), s]
elsif args.length == 1
args + [s]
else
["", s]
end
end
##
# parse diff
#
# >>> diff("a - b")
# ((diff a b) '')
def diff(s)
debug("diff") {"(#{s.inspect})"}
e1, s = depth {postfix(s)}
debug {"=> postfix returned #{[e1, s].inspect}"}
unless e1.to_s.empty?
unless s.to_s.empty?
t, ss = depth {terminal(s)}
debug {"diff #{[t, ss].inspect}"}
if t.is_a?(Array) && t.first == :diff
s = ss
e2, s = primary(s)
unless e2.to_s.empty?
return [[:diff, e1, e2], s]
else
error("diff", "Syntax Error")
raise SyntaxError, "diff missing second operand"
end
end
end
end
[e1, s]
end
##
# parse postfix
#
# >>> postfix("a b c")
# (a ' b c')
#
# >>> postfix("a? b c")
# ((opt, a) ' b c')
def postfix(s)
debug("postfix") {"(#{s.inspect})"}
e, s = depth {primary(s)}
debug {"=> primary returned #{[e, s].inspect}"}
return ["", s] if e.to_s.empty?
if !s.to_s.empty?
t, ss = depth {terminal(s)}
debug {"=> #{[t, ss].inspect}"}
if t.is_a?(Array) && [:opt, :star, :plus].include?(t.first)
return [[t.first, e], ss]
end
end
[e, s]
end
##
# parse primary
#
# >>> primary("a b c")
# (a ' b c')
def primary(s)
debug("primary") {"(#{s.inspect})"}
t, s = depth {terminal(s)}
debug {"=> terminal returned #{[t, s].inspect}"}
if t.is_a?(Symbol) || t.is_a?(String)
[t, s]
elsif %w(range hex).map(&:to_sym).include?(t.first)
[t, s]
elsif t.first == :"("
e, s = depth {expression(s)}
debug {"=> expression returned #{[e, s].inspect}"}
[e, s]
else
["", s]
end
end
##
# parse one terminal; return the terminal and the remaining string
#
# A terminal is represented as a tuple whose 1st item gives the type;
# some types have additional info in the tuple.
#
# @example
# >>> terminal("'abc' def")
# ('abc' ' def')
#
# >>> terminal("[0-9]")
# ((range '0-9') '')
# >>> terminal("#x00B7")
# ((hex '#x00B7') '')
# >>> terminal ("\[#x0300-#x036F\]")
# ((range '#x0300-#x036F') '')
# >>> terminal("\[^<>'{}|^`\]-\[#x00-#x20\]")
# ((range "^<>'{}|^`") '-\[#x00-#x20\]')
def terminal(s)
s = s.strip
#STDERR.puts s.inspect
case m = s[0,1]
when '"', "'" # STRING1 or STRING2
l, s = s[1..-1].split(m.rstrip, 2)
[Unescape.unescape_string(l), s]
when '[' # RANGE, O_RANGE
l, s = s[1..-1].split(/(?<=[^\\])\]/, 2)
[[:range, Unescape.unescape_string(l)], s]
when '#' # HEX
s.match(/(#x\h+)(.*)$/)
l, s = $1, $2
[[:hex, l], s]
when /[\w\.]/ # SYMBOL
s.match(/([\w\.]+)(.*)$/)
l, s = $1, $2
[l.to_sym, s]
when '-'
[[:diff], s[1..-1]]
when '?'
[[:opt], s[1..-1]]
when '|'
[[:alt], s[1..-1]]
when '+'
[[:plus], s[1..-1]]
when '*'
[[:star], s[1..-1]]
when /[\(\)]/ # '(' or ')'
[[m.to_sym], s[1..-1]]
else
error("terminal", "unrecognized terminal: #{s.inspect}")
raise SyntaxError, "unrecognized terminal: #{s.inspect}"
end
end
end
end