Class: Pushdown::State

Inherits:
Object
  • Object
show all
Extended by:
Loggability
Defined in:
lib/pushdown/state.rb

Overview

A componented state object in a Pushdown automaton

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data = nil) ⇒ State

Set up new States with an optional data object.



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# File 'lib/pushdown/state.rb', line 61

def initialize( data=nil )
  @data = data
end

Instance Attribute Details

#data ⇒ Object (readonly)

The state data object that was used to create the State (if any)



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# File 'lib/pushdown/state.rb', line 72

def data
  @data
end

#transitions ⇒ Object (readonly)

Allow introspection on declared transitions



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# File 'lib/pushdown/state.rb', line 22

def transitions
  @transitions
end

Class Method Details

.inherited(subclass) ⇒ Object

Inheritance callback – allow subclasses to be instantiated, and add some class-instance data to them.



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# File 'lib/pushdown/state.rb', line 27

def self::inherited( subclass )
  super

  subclass.public_class_method( :new )
  subclass.instance_variable_set( :@transitions, {} )
end

.register_transition(type) ⇒ Object

Register a transition type declaration method.



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# File 'lib/pushdown/state.rb', line 40

def self::register_transition( type )
  type = type.to_sym
  meth = lambda do |transition_name, *args|
    self.transitions[ transition_name ] = [ type, *args ]
  end

  method_name = "transition_%s" % [ type ]
  self.log.info "Setting up transition declaration method %p" % [ method_name ]
  define_singleton_method( method_name, &meth )
end

.type_name ⇒ Object

Return the transition’s type as a lowercase Symbol, such as that specified in transition declarations.



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# File 'lib/pushdown/state.rb', line 54

def self::type_name
  class_name = self.name or return :anonymous
  return class_name.sub( /.*::/, '' ).downcase.to_sym
end

Instance Method Details

#description ⇒ Object

Return a description of the State as an engine phrase.



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# File 'lib/pushdown/state.rb', line 145

def description
  return "%#x" % [ self.class.object_id ] unless self.class.name
  return self.class.name.sub( /.*::/, '' ).
    gsub( /([A-Z])([A-Z])/ ) { "#$1 #$2" }.
    gsub( /([a-z])([A-Z])/ ) { "#$1 #$2" }.downcase
end

#on_event(event, *args) ⇒ Object

Event callback – called by the automaton when its #on_<stackname>_event method is called. This method can return a Transition or a Symbol which maps to one.



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# File 'lib/pushdown/state.rb', line 110

def on_event( event, *args )
  return nil # no-op
end

#on_pause ⇒ Object

Stack callback – called when another state is pushed over this one.



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# File 'lib/pushdown/state.rb', line 92

def on_pause
  return nil # no-op
end

#on_resume ⇒ Object

Stack callback – called when another state is popped off from in front of this one, making it the current state.



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# File 'lib/pushdown/state.rb', line 99

def on_resume
  return nil # no-op
end

#on_start ⇒ Object

Stack callback – called when the state is added to the stack.



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# File 'lib/pushdown/state.rb', line 80

def on_start
  return nil # no-op
end

#on_stop ⇒ Object

Stack callback – called when the state is removed from the stack.



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# File 'lib/pushdown/state.rb', line 86

def on_stop
  return nil # no-op
end

#shadow_update(*data) ⇒ Object

State callback – interval callback called when the state is on the stack, even when the state is not the current one.



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# File 'lib/pushdown/state.rb', line 128

def shadow_update( *data )
  return nil # no-op
end

#transition(transition_name, automaton, stack_name) ⇒ Object

Create a new instance of Pushdown::Transition named transition_name that has been declared using one of the Transition Declaration methods.



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# File 'lib/pushdown/state.rb', line 155

def transition( transition_name, automaton, stack_name )
  self.log.debug "Looking up the %p transition for %p via %p" %
    [ transition_name, self, automaton ]

  transition_type, state_class_name = self.class.transitions[ transition_name ]
  raise "no such transition %p for %p" % [ transition_name, self.class ] unless transition_type

  if state_class_name
    state_class = automaton.class.pushdown_state_class( stack_name, state_class_name )
    state_data = self.data

    return Pushdown::Transition.
      create( transition_type, transition_name, state_class, state_data )
  else
    return Pushdown::Transition.create( transition_type, transition_name )
  end
end

#type_name ⇒ Object

Return the transition’s type as a lowercase Symbol, such as that specified in transition declarations.



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# File 'lib/pushdown/state.rb', line 139

def type_name
  return self.class.type_name
end

#update(*data) ⇒ Object

State callback – interval callback called when the state is the current one. This method can return a Transition or a Symbol which maps to one.



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# File 'lib/pushdown/state.rb', line 121

def update( *data )
  return nil # no-op
end