Class: Porolog::Goal

Inherits:
Object show all
Defined in:
lib/porolog/goal.rb

Overview

A Porolog::Goal finds solutions for specific Arguments of a Predicate.

Defined Under Namespace

Classes: DefinitionError, Error, NotVariableError

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(arguments, calling_goal = nil) ⇒ Goal

Initializes and registers the Goal.



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# File 'lib/porolog/goal.rb', line 59

def initialize(arguments, calling_goal = nil)
  @@goals << self
  @@goal_count += 1
  
  @arguments    = arguments
  @terminate    = false
  @calling_goal = calling_goal
  @variables    = {}
  @values       = {}
  @result       = nil
  @description  = "Solve #{arguments.inspect}"
  @log          = []
  
  @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
  @solutions = []
end

Instance Attribute Details

#arguments ⇒ Porolog::Arguments 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

#calling_goal ⇒ Porolog::Goal? 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

#description ⇒ String 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

#index ⇒ Integer? 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

#log ⇒ Array<String> 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

#result ⇒ Boolean 



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# File 'lib/porolog/goal.rb', line 27

class Goal
  
  # Error class for rescuing or detecting any Goal error.
  class Error             < PorologError ; end
  # Error class indicating an unexpected type of Rule definition.
  class DefinitionError   < Error        ; end
  # Error class indicating a non-Variable was attempted to be instantiated.
  class NotVariableError  < Error        ; end
  
  # Clears all goals and ensures they are deleted.
  # @return [Boolean] success
  def self.reset
    @@goals ||= []
    goals = @@goals
    @@goals = []
    @@goal_count = 0
    goals.map(&:deleted?)
    true
  end
  
  # @return [Integer] the number of goals created
  def self.goal_count
    @@goal_count
  end
  
  reset
  
  attr_accessor :calling_goal, :arguments, :index, :result, :description, :log
  
  # Initializes and registers the Goal.
  # @param arguments [Porolog::Arguments] the Predicate Arguments that this Goal is to solve.
  # @param calling_goal [Porolog::Goal] the parent Goal if this Goal is a subgoal.
  def initialize(arguments, calling_goal = nil)
    @@goals << self
    @@goal_count += 1
    
    @arguments    = arguments
    @terminate    = false
    @calling_goal = calling_goal
    @variables    = {}
    @values       = {}
    @result       = nil
    @description  = "Solve #{arguments.inspect}"
    @log          = []
    
    @arguments = @arguments.dup(self) if @arguments.is_a?(Arguments)
    @solutions = []
  end
  
  # @return [Array<Porolog::Goal>] the calling chain for this goal.
  def ancestors
    ancestors = []
    goal      = self
    
    while goal
      ancestors << goal
      goal = goal.calling_goal
    end
    
    ancestors.reverse
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the calling chain for this goal as a String.
  def ancestry
    indent = -1
    ancestors.map do |goal|
      indent += 1
      "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
    end.join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [String] the id of the goal.
  def myid
    "Goal#{(@@goals.index(self) || -1000) + 1}"
  end
  
  # @return [String] pretty representation.
  def inspect
    "#{myid} -- #{description}"
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Porolog::Goal>]
  def self.goals
    @@goals
  end
  
  # Delete the Goal
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def delete!
    @@goals.delete(self)
    deleted?
  end
  
  # @return [Boolean] whether the Goal has been deleted (memoized)
  def deleted?
    @deleted ||= check_deleted
    @deleted
  end
  
  # Determines whether the Goal has been deleted and removes its Variables and Values if it has.
  # @return [Boolean] whether the Goal has been deleted
  def check_deleted
    return false if @@goals.include?(self)
    
    @variables.delete_if do |_name,variable|
      variable.remove
      true
    end
    
    @values.delete_if do |_name,value|
      value.remove
      true
    end
    
    true
  end
  
  # Sets that the goal should no longer search any further rules for the current predicate
  # once the current rule has finished being evaluated.
  # This method implements the :CUT rule.
  # That is, backtracking does not go back past the point of the cut.
  # @return [Boolean] true.
  def terminate!
    @log << 'terminating'
    @terminate = true
  end
  
  # @return [Boolean] whether the goal has been cut.
  def terminated?
    @terminate
  end
  
  # Converts all embedded Symbols to Variables within this Goal.
  # @param object [Object] the object to variablise.
  # @return [Object] the variablised object.
  def variablise(object)
    case object
      when Symbol,Variable
        variable(object)
      when Array
        object.map{|element| variablise(element) }
      when Arguments
        object.dup(self)
      when Tail
        Tail.new variablise(object.value)
      when Value
        object
      when NilClass
        nil
      else
        if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
          object
        else
          value(object)
        end
    end
  end
  
  alias [] variablise
  
  # @return [Hash{Symbol => Object}] the Variables and their current values of this Goal
  def variables
    @variables.keys.each_with_object({}){|variable,variable_list|
      value = value_of(variable).value.value
      if value.is_a?(Variable)
        variable_list[variable] = nil
      elsif value.is_a?(Array)
        variable_list[variable] = value.clean
      else
        variable_list[variable] = value
      end
    }
  end
  
  # A convenience method for testing/debugging.
  # @return [String] a tree representation of all the instantiations of this goal's variables.
  def inspect_variables
    @variables.values.map(&:inspect_with_instantiations).join("\n")
  end
  
  # A convenience method for testing/debugging.
  # @return [Array<Object>] the values instantiated for this goal.
  def values
    @values.values.map(&:value)
  end
  
  # Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.
  # @param name [Object] name of variable or variable
  # @return [Porolog::Variable, Object] a variable of the goal or the original parameter
  def variable(name)
    return name unless name.is_a?(Symbol) || name.is_a?(Variable)
    
    if name.is_a?(Variable)
      variable = name
      @variables[variable.name] = variable if variable.goal == self
      return variable
    end
    
    @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
    @variables[name]
  end
  
  # @param value [Object] the value that needs to be associated with this Goal.
  # @return [Porolog::Value] a Value, ensuring it has been associated with this Goal so that it can be uninstantiated.
  def value(value)
    @values[value] ||= Value.new(value, self)
    @values[value]
  end
  
  # Returns the value of the indicated variable or value
  # @param name [Symbol, Object] name of the variable or value
  # @param index [Object] index is not yet used
  # @param visited [Array] used to avoid infinite recursion
  # @return [Object] the value
  def value_of(name, index = nil, visited = [])
    variable(name).value(visited)
  end
  
  # Returns the values of an Object.  For most objects, this will basically just be the object.
  # For Arrays, an Array will be returned where the elements are the value of the elements.
  # @param object [Object] the Object to find the values of.
  # @return [Object,Array<Object>] the value(s) of the object.
  def values_of(object)
    case object
      when Array
        object.map{|element| values_of(element) }
      when Variable,Symbol,Value
        value_of(object)
      when Tail
        # TODO: This needs to splat outwards; in the meantime, it splats just the first.
        value_of(object.value).first
      else
        object
    end
  end
  
  # Finds all possible solutions to the Predicate for the specific Arguments.
  # @param max_solutions [Integer] if provided, the search is stopped once the number of solutions has been found
  # @return [Array<Hash{Symbol => Object}>]
  def solve(max_solutions = nil)
    return @solutions unless @arguments
    
    predicate = @arguments.predicate
    
    predicate&.satisfy(self) do |goal|
      # TODO: Refactor to overrideable method (or another solution, say a lambda)
      
      @solutions << variables
      @log << "SOLUTION: #{variables}"
      @log << goal.ancestry
      @log << goal.inspect_variables
      
      return @solutions if max_solutions && @solutions.size >= max_solutions
    end
    
    @solutions
  end
  
  # Solves the goal but not as the root goal for a query.
  # That is, solves an intermediate goal.
  # @param block [Proc] code to perform when the Goal is satisfied.
  # @return [Boolean] whether the definition was satisfied.
  def satisfy(&block)
    return false unless @arguments
    
    predicate = @arguments.predicate
    
    satisfied = false
    predicate&.satisfy(self) do |subgoal|
      subgoal_satisfied = block.call(subgoal)
      satisfied ||= subgoal_satisfied
    end
    satisfied
  end
  
  # Instantiates a Variable to another Variable or Value, for this Goal.
  # @param name [Symbol,Porolog::Variable,Object] the name that references the variable to be instantiated.
  # @param other [Object] the value that the variable is to be instantiated to.
  # @param other_goal [Porolog::Goal,nil] the Goal of the other value.
  # @return [Porolog::Instantiation] the instantiation.
  def instantiate(name, other, other_goal = self)
    variable = self.variable(name)
    
    other = if other.type == :variable
      other_goal.variable(other)
    else
      other_goal.value(other)
    end
    
    variable.instantiate(other)
  end
  
  # Inherits variables and their instantiations from another goal.
  # @param other_goal [Porolog::Goal,nil] the Goal to inherit variables from.
  # @return [Boolean] whether the variables could be inherited (unified).
  def inherit_variables(other_goal = @calling_goal)
    return true unless other_goal
    
    unified      = true
    unifications = []
    variables    = (
      other_goal.arguments.variables +
      other_goal.variables.keys +
      self.arguments.variables
    ).map(&:to_sym).uniq
    
    variables.each do |variable|
      name = variable
      
      unification = Porolog::unify(name, name, other_goal, self)
      unified   &&= !!unification
      if unified
        unifications += unification
      else
        #:nocov:
        self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
        break
        #:nocov:
      end
    end
    unified &&= Porolog::instantiate_unifications(unifications) if unified
    
    unified
  end
  
end

Class Method Details

.goal_count ⇒ Integer 



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# File 'lib/porolog/goal.rb', line 48

def self.goal_count
  @@goal_count
end

.goals ⇒ Array<Porolog::Goal>

A convenience method for testing/debugging.



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# File 'lib/porolog/goal.rb', line 112

def self.goals
  @@goals
end

.reset ⇒ Boolean

Clears all goals and ensures they are deleted.



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# File 'lib/porolog/goal.rb', line 38

def self.reset
  @@goals ||= []
  goals = @@goals
  @@goals = []
  @@goal_count = 0
  goals.map(&:deleted?)
  true
end

Instance Method Details

#ancestors ⇒ Array<Porolog::Goal> 



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# File 'lib/porolog/goal.rb', line 77

def ancestors
  ancestors = []
  goal      = self
  
  while goal
    ancestors << goal
    goal = goal.calling_goal
  end
  
  ancestors.reverse
end

#ancestry ⇒ String

A convenience method for testing/debugging.



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# File 'lib/porolog/goal.rb', line 91

def ancestry
  indent = -1
  ancestors.map do |goal|
    indent += 1
    "#{'  ' * indent}#{goal.myid} -- #{goal.description}  #{goal.variables.inspect}"
  end.join("\n")
end

#check_deleted ⇒ Boolean

Determines whether the Goal has been deleted and removes its Variables and Values if it has.



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# File 'lib/porolog/goal.rb', line 131

def check_deleted
  return false if @@goals.include?(self)
  
  @variables.delete_if do |_name,variable|
    variable.remove
    true
  end
  
  @values.delete_if do |_name,value|
    value.remove
    true
  end
  
  true
end

#delete! ⇒ Boolean

Delete the Goal



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# File 'lib/porolog/goal.rb', line 118

def delete!
  @@goals.delete(self)
  deleted?
end

#deleted? ⇒ Boolean 



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# File 'lib/porolog/goal.rb', line 124

def deleted?
  @deleted ||= check_deleted
  @deleted
end

#inherit_variables(other_goal = @calling_goal) ⇒ Boolean

Inherits variables and their instantiations from another goal.



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# File 'lib/porolog/goal.rb', line 325

def inherit_variables(other_goal = @calling_goal)
  return true unless other_goal
  
  unified      = true
  unifications = []
  variables    = (
    other_goal.arguments.variables +
    other_goal.variables.keys +
    self.arguments.variables
  ).map(&:to_sym).uniq
  
  variables.each do |variable|
    name = variable
    
    unification = Porolog::unify(name, name, other_goal, self)
    unified   &&= !!unification
    if unified
      unifications += unification
    else
      #:nocov:
      self.log << "Couldn't unify: #{name.inspect} WITH #{other_goal.myid} AND #{self.myid}"
      break
      #:nocov:
    end
  end
  unified &&= Porolog::instantiate_unifications(unifications) if unified
  
  unified
end

#inspect ⇒ String 



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# File 'lib/porolog/goal.rb', line 106

def inspect
  "#{myid} -- #{description}"
end

#inspect_variables ⇒ String

A convenience method for testing/debugging.



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# File 'lib/porolog/goal.rb', line 206

def inspect_variables
  @variables.values.map(&:inspect_with_instantiations).join("\n")
end

#instantiate(name, other, other_goal = self) ⇒ Porolog::Instantiation

Instantiates a Variable to another Variable or Value, for this Goal.



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# File 'lib/porolog/goal.rb', line 310

def instantiate(name, other, other_goal = self)
  variable = self.variable(name)
  
  other = if other.type == :variable
    other_goal.variable(other)
  else
    other_goal.value(other)
  end
  
  variable.instantiate(other)
end

#myid ⇒ String

A convenience method for testing/debugging.



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# File 'lib/porolog/goal.rb', line 101

def myid
  "Goal#{(@@goals.index(self) || -1000) + 1}"
end

#satisfy(&block) ⇒ Boolean

Solves the goal but not as the root goal for a query. That is, solves an intermediate goal.



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# File 'lib/porolog/goal.rb', line 292

def satisfy(&block)
  return false unless @arguments
  
  predicate = @arguments.predicate
  
  satisfied = false
  predicate&.satisfy(self) do |subgoal|
    subgoal_satisfied = block.call(subgoal)
    satisfied ||= subgoal_satisfied
  end
  satisfied
end

#solve(max_solutions = nil) ⇒ Array<Hash{Symbol => Object}>

Finds all possible solutions to the Predicate for the specific Arguments.



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# File 'lib/porolog/goal.rb', line 269

def solve(max_solutions = nil)
  return @solutions unless @arguments
  
  predicate = @arguments.predicate
  
  predicate&.satisfy(self) do |goal|
    # TODO: Refactor to overrideable method (or another solution, say a lambda)
    
    @solutions << variables
    @log << "SOLUTION: #{variables}"
    @log << goal.ancestry
    @log << goal.inspect_variables
    
    return @solutions if max_solutions && @solutions.size >= max_solutions
  end
  
  @solutions
end

#terminate! ⇒ Boolean

Sets that the goal should no longer search any further rules for the current predicate once the current rule has finished being evaluated. This method implements the :CUT rule. That is, backtracking does not go back past the point of the cut.



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# File 'lib/porolog/goal.rb', line 152

def terminate!
  @log << 'terminating'
  @terminate = true
end

#terminated? ⇒ Boolean 



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# File 'lib/porolog/goal.rb', line 158

def terminated?
  @terminate
end

#value(value) ⇒ Porolog::Value 



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# File 'lib/porolog/goal.rb', line 234

def value(value)
  @values[value] ||= Value.new(value, self)
  @values[value]
end

#value_of(name, index = nil, visited = []) ⇒ Object

Returns the value of the indicated variable or value



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# File 'lib/porolog/goal.rb', line 244

def value_of(name, index = nil, visited = [])
  variable(name).value(visited)
end

#values ⇒ Array<Object>

A convenience method for testing/debugging.



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# File 'lib/porolog/goal.rb', line 212

def values
  @values.values.map(&:value)
end

#values_of(object) ⇒ Object+

Returns the values of an Object. For most objects, this will basically just be the object. For Arrays, an Array will be returned where the elements are the value of the elements.



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# File 'lib/porolog/goal.rb', line 252

def values_of(object)
  case object
    when Array
      object.map{|element| values_of(element) }
    when Variable,Symbol,Value
      value_of(object)
    when Tail
      # TODO: This needs to splat outwards; in the meantime, it splats just the first.
      value_of(object.value).first
    else
      object
  end
end

#variable(name) ⇒ Porolog::Variable, Object

Finds or tries to create a variable in the goal (as much as possible) otherwise passes the parameter back.



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# File 'lib/porolog/goal.rb', line 219

def variable(name)
  return name unless name.is_a?(Symbol) || name.is_a?(Variable)
  
  if name.is_a?(Variable)
    variable = name
    @variables[variable.name] = variable if variable.goal == self
    return variable
  end
  
  @variables[name] ||= (name.is_a?(Variable) && name || Variable.new(name, self))
  @variables[name]
end

#variables ⇒ Hash{Symbol => Object} 



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# File 'lib/porolog/goal.rb', line 191

def variables
  @variables.keys.each_with_object({}){|variable,variable_list|
    value = value_of(variable).value.value
    if value.is_a?(Variable)
      variable_list[variable] = nil
    elsif value.is_a?(Array)
      variable_list[variable] = value.clean
    else
      variable_list[variable] = value
    end
  }
end

#variablise(object) ⇒ Object Also known as: []

Converts all embedded Symbols to Variables within this Goal.



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# File 'lib/porolog/goal.rb', line 165

def variablise(object)
  case object
    when Symbol,Variable
      variable(object)
    when Array
      object.map{|element| variablise(element) }
    when Arguments
      object.dup(self)
    when Tail
      Tail.new variablise(object.value)
    when Value
      object
    when NilClass
      nil
    else
      if [UNKNOWN_TAIL, UNKNOWN_ARRAY].include?(object)
        object
      else
        value(object)
      end
  end
end