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require 'action_dispatch/journey/gtg/transition_table'
module ActionDispatch
module Journey # :nodoc:
module GTG # :nodoc:
class Builder # :nodoc:
DUMMY = Nodes::Dummy.new
attr_reader :root, :ast, :endpoints
def initialize(root)
@root = root
@ast = Nodes::Cat.new root, DUMMY
@followpos = nil
end
def transition_table
dtrans = TransitionTable.new
marked = {}
state_id = Hash.new { |h,k| h[k] = h.length }
start = firstpos(root)
dstates = [start]
until dstates.empty?
s = dstates.shift
next if marked[s]
marked[s] = true # mark s
s.group_by { |state| symbol(state) }.each do |sym, ps|
u = ps.flat_map { |l| followpos(l) }
next if u.empty?
if u.uniq == [DUMMY]
from = state_id[s]
to = state_id[Object.new]
dtrans[from, to] = sym
dtrans.add_accepting(to)
ps.each { |state| dtrans.add_memo(to, state.memo) }
else
dtrans[state_id[s], state_id[u]] = sym
if u.include?(DUMMY)
to = state_id[u]
accepting = ps.find_all { |l| followpos(l).include?(DUMMY) }
accepting.each { |accepting_state|
dtrans.add_memo(to, accepting_state.memo)
}
dtrans.add_accepting(state_id[u])
end
end
dstates << u
end
end
dtrans
end
def nullable?(node)
case node
when Nodes::Group
true
when Nodes::Star
true
when Nodes::Or
node.children.any? { |c| nullable?(c) }
when Nodes::Cat
nullable?(node.left) && nullable?(node.right)
when Nodes::Terminal
!node.left
when Nodes::Unary
nullable?(node.left)
else
raise ArgumentError, 'unknown nullable: %s' % node.class.name
end
end
def firstpos(node)
case node
when Nodes::Star
firstpos(node.left)
when Nodes::Cat
if nullable?(node.left)
firstpos(node.left) | firstpos(node.right)
else
firstpos(node.left)
end
when Nodes::Or
node.children.flat_map { |c| firstpos(c) }.uniq
when Nodes::Unary
firstpos(node.left)
when Nodes::Terminal
nullable?(node) ? [] : [node]
else
raise ArgumentError, 'unknown firstpos: %s' % node.class.name
end
end
def lastpos(node)
case node
when Nodes::Star
firstpos(node.left)
when Nodes::Or
node.children.flat_map { |c| lastpos(c) }.uniq
when Nodes::Cat
if nullable?(node.right)
lastpos(node.left) | lastpos(node.right)
else
lastpos(node.right)
end
when Nodes::Terminal
nullable?(node) ? [] : [node]
when Nodes::Unary
lastpos(node.left)
else
raise ArgumentError, 'unknown lastpos: %s' % node.class.name
end
end
def followpos(node)
followpos_table[node]
end
private
def followpos_table
@followpos ||= build_followpos
end
def build_followpos
table = Hash.new { |h, k| h[k] = [] }
@ast.each do |n|
case n
when Nodes::Cat
lastpos(n.left).each do |i|
table[i] += firstpos(n.right)
end
when Nodes::Star
lastpos(n).each do |i|
table[i] += firstpos(n)
end
end
end
table
end
def symbol(edge)
case edge
when Journey::Nodes::Symbol
edge.regexp
else
edge.left
end
end
end
end
end
end
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