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require 'action_dispatch/journey/nfa/dot'
module ActionDispatch
module Journey # :nodoc:
module NFA # :nodoc:
class TransitionTable # :nodoc:
include Journey::NFA::Dot
attr_accessor :accepting
attr_reader :memos
def initialize
@table = Hash.new { |h,f| h[f] = {} }
@memos = {}
@accepting = nil
@inverted = nil
end
def accepting?(state)
accepting == state
end
def accepting_states
[accepting]
end
def add_memo(idx, memo)
@memos[idx] = memo
end
def memo(idx)
@memos[idx]
end
def []=(i, f, s)
@table[f][i] = s
end
def merge(left, right)
@memos[right] = @memos.delete(left)
@table[right] = @table.delete(left)
end
def states
(@table.keys + @table.values.flat_map(&:keys)).uniq
end
# Returns a generalized transition graph with reduced states. The states
# are reduced like a DFA, but the table must be simulated like an NFA.
#
# Edges of the GTG are regular expressions.
def generalized_table
gt = GTG::TransitionTable.new
marked = {}
state_id = Hash.new { |h,k| h[k] = h.length }
alphabet = self.alphabet
stack = [eclosure(0)]
until stack.empty?
state = stack.pop
next if marked[state] || state.empty?
marked[state] = true
alphabet.each do |alpha|
next_state = eclosure(following_states(state, alpha))
next if next_state.empty?
gt[state_id[state], state_id[next_state]] = alpha
stack << next_state
end
end
final_groups = state_id.keys.find_all { |s|
s.sort.last == accepting
}
final_groups.each do |states|
id = state_id[states]
gt.add_accepting(id)
save = states.find { |s|
@memos.key?(s) && eclosure(s).sort.last == accepting
}
gt.add_memo(id, memo(save))
end
gt
end
# Returns set of NFA states to which there is a transition on ast symbol
# +a+ from some state +s+ in +t+.
def following_states(t, a)
Array(t).flat_map { |s| inverted[s][a] }.uniq
end
# Returns set of NFA states to which there is a transition on ast symbol
# +a+ from some state +s+ in +t+.
def move(t, a)
Array(t).map { |s|
inverted[s].keys.compact.find_all { |sym|
sym === a
}.map { |sym| inverted[s][sym] }
}.flatten.uniq
end
def alphabet
inverted.values.flat_map(&:keys).compact.uniq.sort_by(&:to_s)
end
# Returns a set of NFA states reachable from some NFA state +s+ in set
# +t+ on nil-transitions alone.
def eclosure(t)
stack = Array(t)
seen = {}
children = []
until stack.empty?
s = stack.pop
next if seen[s]
seen[s] = true
children << s
stack.concat(inverted[s][nil])
end
children.uniq
end
def transitions
@table.flat_map { |to, hash|
hash.map { |from, sym| [from, sym, to] }
}
end
private
def inverted
return @inverted if @inverted
@inverted = Hash.new { |h, from|
h[from] = Hash.new { |j, s| j[s] = [] }
}
@table.each { |to, hash|
hash.each { |from, sym|
if sym
sym = Nodes::Symbol === sym ? sym.regexp : sym.left
end
@inverted[from][sym] << to
}
}
@inverted
end
end
end
end
end
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