Class: ToknInternal::State

Inherits:
Object
  • Object
show all
Defined in:
lib/tokn/state.rb

Overview

A state within a state machine (NFA or DFA); also, various utility functions for manipulating state machines. Observe that a state machine can be referred to by its start state.

Each state has a set of directed edges to other states, where each edge is labelled with a CodeSet.

It also has a unique id (unique within a particular state machine), and a (boolean) final state flag.

For debug purposes, both the state and its edges can be labelled.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(id) ⇒ State

Returns a new instance of State.



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# File 'lib/tokn/state.rb', line 51

def initialize(id) 
  @edges = [] 
  @id = id
end

Instance Attribute Details

#edges ⇒ Object (readonly)

Edges are a list of [label:CharSetRange, dest:State] pairs



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# File 'lib/tokn/state.rb', line 26

def edges
  @edges
end

#finalState ⇒ Object Also known as: finalState?

Returns the value of attribute finalState.



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# File 'lib/tokn/state.rb', line 21

def finalState
  @finalState
end

#id ⇒ Object

Returns the value of attribute id.



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# File 'lib/tokn/state.rb', line 20

def id
  @id
end

#label ⇒ Object

Returns the value of attribute label.



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# File 'lib/tokn/state.rb', line 23

def label
  @label
end

Class Method Details

.dumpNFA(st) ⇒ Object

Produce a readable description of an NFA, for debug purposes

> st start state



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# File 'lib/tokn/state.rb', line 32

def self.dumpNFA(st)
  str = "NFA:\n"
  map,_,_ = st.reachableStates
  map.each do |s| 
    str += " "+d(s)+"\n"
    str += "  edges= "+d(s.edges)+"\n"
    s.edges.each{ |lbl,dest| str += "   "+d(lbl)+"  ==> "+d(dest)+"\n"}
  end
  str
end

.normalizeStates(startState) ⇒ Object

Normalize a state machine.

For each state:

[] merge edges that go to a common state
[] delete edges that have empty labels
[] sort edges by destination state ids

> start state



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# File 'lib/tokn/state.rb', line 96

def self.normalizeStates(startState)
  stateSet, _,_ = startState.reachableStates
  stateSet.map{|s| s.normalize}
end

Instance Method Details

#addEdge(codeSet, destState) ⇒ Object

Add an edge

codeSet : the character codes to label it with
destState : destination state



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# File 'lib/tokn/state.rb', line 64

def addEdge(codeSet,destState)
  @edges.push([codeSet, destState])
end

#addEps(destState) ⇒ Object

Add a e-transition edge

destState : destination state



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# File 'lib/tokn/state.rb', line 71

def addEps(destState)
  addEdge(CodeSet.new(EPSILON), destState)
end

#clearEdges ⇒ Object 



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# File 'lib/tokn/state.rb', line 56

def clearEdges
  @edges.clear
end

#duplicateNFA(dupBaseId = nil) ⇒ Object

Duplicate the NFA reachable from this state, possibly with new ids

> dupBaseId : lowest id to use for duplicate; if nil, uses

next available id

< [ map of original states => duplicate states;

1 + highest id in new NFA ]



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# File 'lib/tokn/state.rb', line 198

def duplicateNFA(dupBaseId = nil)
  oldStates, oldMinId, oldMaxId = reachableStates()
  dupBaseId ||= oldMaxId
  
   
  oldToNewStateMap = {}
  
  oldStates.each do |s|
    s2 = State.new((s.id - oldMinId) + dupBaseId)
    s2.finalState = s.finalState?
    s2.label = s.label
    
    oldToNewStateMap[s] = s2
  end
  
  oldStates.each do |s|
    s2 = oldToNewStateMap[s]
    s.edges.each{ |lbl,dest|  s2.addEdge(lbl, oldToNewStateMap[dest])}
  end
  
  [oldToNewStateMap, (oldMaxId - oldMinId) + dupBaseId]
end

#eql?(other) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/tokn/state.rb', line 47

def eql?(other)
  return id == other.id
end

#generatePDF(dir = nil, title = "nfa") ⇒ Object

Generate a PDF of the state machine; Makes a system call to the dot utility to convert a .dot file to a .pdf



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# File 'lib/tokn/state.rb', line 105

def generatePDF(dir = nil, title = "nfa")
  stateList = {}
  
  startState = self
  genAux( stateList, startState)
  
  g = ""
  g += "digraph "+title+" {\n"
  g += " '' [shape=none]\n"
  
  stateList.each_value do |s| 
    g += " '" + s.name + "' [shape="
    if s.finalState?
      g += "doubleoctagon"
    else
      g += "octagon"
    end
    g += "]\n"
  end

  g += "\n"
  g += " '' -> '" + startState.name + "'\n"
  stateList.each_value do |s| 
    s.edges.each do |crs, s2|
      g += " '"+s.name+"' -> '" + s2.name + "' [label='"
      g += d(crs)
      g += "'][fontname=Courier][fontsize=12]\n"
    end
  end

  g += "\n}\n"
  g.gsub!( /'/, '"' )
  
  dotToPDF(g,title,dir)
end

#hash ⇒ Object 



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# File 'lib/tokn/state.rb', line 43

def hash
  return @id
end

#inspect ⇒ Object 



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# File 'lib/tokn/state.rb', line 75

def inspect   
  name
end

#name ⇒ Object 



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# File 'lib/tokn/state.rb', line 79

def name
  nm = 'S' + d(id)
  if label
    nm += ": "+label
  end
  nm
end

#normalize ⇒ Object

Normalize a state

[] merge edges that go to a common state
[] delete edges that have empty labels
[] sort edges by destination state ids



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# File 'lib/tokn/state.rb', line 148

def normalize()
  
  db = false
  
  !db || pr("\n\nnormalize state:\n  %s\nedges=\n%s\n",d(self),d(@edges))
  
  @edges.sort!{|x,y| 
    label1,dest1 = x
    label2,dest2 = y
    dest1.id <=> dest2.id
  }
  !db || pr(" sorted edges: %s\n",d(@edges))
  
  newEdges = []
  prevLabel, prevDest = nil,nil
  
  edges.each do |label,dest|
    !db || pr("  processing edge  %s,  %s\n",d(label),d(dest))
  
    if prevDest and prevDest.id == dest.id
      # changed = true
      !db || pr("    adding set %s to prevLabel %s...\n",d(label),d(prevLabel))
      prevLabel.addSet(label)
      !db || pr("    ...now %s\n",d(prevLabel))
    else
      if prevDest
        newEdges.push([prevLabel,prevDest])
      end
      # Must start a fresh copy!  Don't want to modify the original label.
      prevLabel = label.makeCopy()
      prevDest = dest
      !db || pr("    pushed onto new edges\n")  
      end
    end
    if prevDest
       newEdges.push([prevLabel,prevDest])
    end
          
  @edges = newEdges
  !db || pr("edges now: %s\n",d(@edges))
end

#reachableStates ⇒ Object

Build set of states reachable from this state

> list of starting states < [ set, set of states reachable from those states

  minId, lowest id in set
  maxId    1 + highest id in set
]



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# File 'lib/tokn/state.rb', line 276

def reachableStates()
  set = Set.new
  stack = []
  stack.push(self)
  
  maxId = nil
  minId = nil
  
  while !stack.empty?
    st = stack.pop
    set.add(st)
    
    if !minId || minId > st.id
      minId = st.id
    end
    if !maxId || maxId <= st.id
      maxId = 1 + st.id
    end
    
    st.edges.each do |lbl, dest|
      if set.add?(dest)
        stack.push(dest)
      end
    end
  end
  [set, minId,  maxId]
end

#reverseNFA ⇒ Object

Construct the reverse of the NFA starting at this state < start state of reversed NFA



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# File 'lib/tokn/state.rb', line 226

def reverseNFA()
  
  stateSet, minId, maxId = reachableStates()
  
  edgeList = []
  
  newStartStateList = []
  newFinalStateList = []
  
  newStateMap = {}
  
  stateSet.each do |s|
      
    u = State.new(s.id)
    newStateMap[u.id] = u
    
    if s.id == self.id
      newFinalStateList.push(u)
      u.finalState = true
    end
    
    if s.finalState?
      newStartStateList.push(u)
    end
    
    s.edges.each {|lbl, dest| edgeList.push([dest.id, s.id, lbl])}
    
  end
  
  edgeList.each do |srcId, destId, lbl|
    srcState = newStateMap[srcId]
    destState = newStateMap[destId]
    srcState.addEdge(lbl, destState)  
  end
  
  # Create a distinguished start node that points to each of the start nodes
  w = State.new(maxId)
  newStartStateList.each {|s| w.addEps(s)}  
  w
end