Module: Porolog::Predicate::Builtin

Defined in:
lib/porolog/predicate/builtin.rb

Overview

The Porolog::Predicate::Builtin module is a collection of the implementations of the builtin predicates. It is possible to define custom builtin predicates. Each builtin requires a goal and a block, and should return the result of

block.call(goal) || false

if the predicate is deemed successful; otherwise, it should return false.

Author:

  • Luis Esteban

Instance Method Summary collapse

Instance Method Details

#append(goal, block, front, back, front_back) ⇒ Boolean

Corresponds to the standard Prolog append predicate. This implements the usual operation of member but also provides the ability instantiate uninstantiated arguments as an instnatiation of the concatenation of the first two arguments. Use:

append([1,2,3], [4,5,6], [1,2,3,4,5,6])
append([1,2,3], [4,5,6], :C)
append([1,2,3], :B, [1,2,3,4,5,6])
append(:A, [4,5,6], [1,2,3,4,5,6])
append(:A, :B, [1,2,3,4,5,6])
append([1,2,3], :B, :C)
append(:A, [4,5,6], :C)
append(:A, :B, :C)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • front (Array, Porolog::Variable) —

    the front portion of the combined front_back argument.

  • back (Array, Porolog::Variable) —

    the back portion of the combined front_back argument.

  • front_back (Array, Porolog::Variable) —

    the combined argument of the front and back arguments.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 594

def append(goal, block, front, back, front_back)
  front       = front.value.value
  back        = back.value.value
  front_back  = front_back.value.value
  
  case [front.type, back.type, front_back.type]
    when [:array, :array, :array]
      satisfied = false
      if front.length + back.length == front_back.length
        unifications   = Porolog::unify(front + back, front_back, goal)
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
      end
      satisfied
      
    when [:array, :array, :variable]
      satisfied = false
      unifications   = Porolog::unify(front + back, front_back, goal)
      instantiations = Porolog::instantiate_unifications(unifications) if unifications
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    when [:array, :variable, :array]
      satisfied = false
      if front.length <= front_back.length
        expected_front = front_back[0...front.length]
        expected_back  = front_back[front.length..-1]
        
        unifications   = Porolog::unify(front, expected_front, goal)
        unifications  += Porolog::unify(back,  expected_back,  goal)     if unifications
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
      end
      satisfied
      
    when [:variable, :array, :array]
      satisfied = false
      if back.length <= front_back.length
        expected_front = front_back[0...-back.length]
        expected_back  = front_back[-back.length..-1]
        
        unifications   = Porolog::unify(front, expected_front, goal)
        unifications  += Porolog::unify(back,  expected_back,  goal)     if unifications
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
      end
      satisfied
      
    when [:variable, :variable, :array]
      satisfied = false
      (front_back.length + 1).times do |i|
        expected_front = front_back[0...i]
        expected_back  = front_back[i..-1]
        
        unifications   = Porolog::unify(front, expected_front, goal)
        unifications  += Porolog::unify(back,  expected_back,  goal)     if unifications
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
        return satisfied if goal.terminated?
      end
      satisfied
      
    when [:array, :variable, :variable]
      satisfied = false
      unifications   = Porolog::unify(front / back, front_back, goal)
      instantiations = Porolog::instantiate_unifications(unifications) if unifications
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    when [:variable, :array, :variable]
      satisfied = false
      instantiation_head = front_back.instantiate(front, nil, :flathead)
      instantiation_tail = front_back.instantiate(back,  nil, :flattail)
      instantiations = [instantiation_head, instantiation_tail].compact
      instantiations = nil if instantiations.empty?
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    when [:variable, :variable, :variable]
      satisfied = false
      instantiation_head = front_back.instantiate(front, nil, :flathead)
      instantiation_tail = front_back.instantiate(back,  nil, :flattail)
      instantiations = [instantiation_head, instantiation_tail].compact
      instantiations = nil if instantiations.empty?
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    else
      false
  end
end

#atom(goal, block, variable) ⇒ Boolean

Corresponds to the standard Prolog atom predicate. It is satisfied if the argument is a String. Use:

atom(:X)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable, Object) —

    the argument to be tested.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 132

def atom(goal, block, variable)
  variable.value.value.is_a?(String) && block.call(goal) || false
end

#atomic(goal, block, variable) ⇒ Boolean

Corresponds to the standard Prolog atomic predicate. It is satisfied if the argument is a String or an Integer. Use:

atomic(:X)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable, Object) —

    the argument to be tested.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 144

def atomic(goal, block, variable)
  variable.value.value.type == :atomic && block.call(goal) || false
end

#between(goal, block, variable, lower, upper) ⇒ Boolean

Does not correspond to a standard Prolog predicate. This is a convenience Predicate to allow efficient control of iteration as well as range comparison. Use:

between(5, 0, 9)
between(:N, 0, 9)
between(:N, :Upper, :Lower)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (String, Integer, Porolog::Variable) —

    the intermediate value or variable.

  • lower (String, Integer) —

    the lower bound of the iteration or range.

  • upper (String, Integer) —

    the upper bound of the iteration or range.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 459

def between(goal, block, variable, lower, upper)
  variable = variable.value.value
  lower    = lower.value.value
  upper    = upper.value.value
  
  case [variable.type, lower.type, upper.type]
    when [:atomic, :atomic, :atomic]
      (lower..upper) === variable && block.call(goal) || false
      
    when [:atomic, :variable, :variable]
      satisfied = false
      lower_instantiation = lower.instantiate(variable)
      upper_instantiation = lower_instantiation && upper.instantiate(variable)
      upper_instantiation && block.call(goal) && (satisfied = true)
      upper_instantiation&.remove
      lower_instantiation&.remove
      satisfied
      
    when [:atomic, :atomic, :variable]
      satisfied = false
      if variable >= lower
        upper_instantiation = upper.instantiate(variable)
        upper_instantiation && block.call(goal) && (satisfied = true)
        upper_instantiation&.remove
      end
      satisfied
      
    when [:atomic, :variable, :atomic]
      satisfied = false
      if variable <= upper
        lower_instantiation = lower.instantiate(variable)
        lower_instantiation && block.call(goal) && (satisfied = true)
        lower_instantiation&.remove
      end
      satisfied
      
    when [:variable, :atomic, :atomic]
      satisfied = false
      (lower..upper).each do |i|
        instantiation = variable.instantiate(i)
        instantiation && block.call(goal) && (satisfied = true) || false
        instantiation&.remove
        return satisfied if goal.terminated?
      end
      satisfied
      
    else
      false
  end
end

#eq(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog == predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) that are equal, or

  • it is provided with two uninstantiaed Variables that are bound to each other.

Variables are not instantiated; however, if they are uninstantiated, they are temporarily instantiated to a unique value to see if they are bound in some way. Use:

eq(:X, :Y)
eq(:name, ['Sam', 'Smith'])

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the equality.

  • y (Object) —

    the right hand side of the equality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 174

def eq(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  case [x.type, y.type]
    when [:variable, :variable]
      equal = false
      temporary_instantiation = x.instantiate UNIQUE_VALUE
      if temporary_instantiation
        equal = y.value.value == UNIQUE_VALUE
        temporary_instantiation.remove
      end
      equal
    else
      x == y
  end && block.call(goal) || false
end

#gtr(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog > predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) where the first is greater than the second.

Variables are not instantiated. Use:

gtr(:X, :Y)
gtr(:X, 3)
gtr(9, :Y)
gtr(:name, 'max')

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the inequality.

  • y (Object) —

    the right hand side of the inequality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 331

def gtr(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  if [x.type, y.type].include?(:variable)
    false
  else
    x > y
  end && block.call(goal) || false
end

#gtreq(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog >= predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) where the first is greater than or equal to the second, or

  • it is provided with two uninstantiaed Variables that are bound to each other.

Variables are not instantiated (except temporarily to test if they are bound). Use:

gtreq(:X, :Y)
gtreq(:X, 3)
gtreq(9, :Y)
gtreq(:name, 'max')

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the inequality.

  • y (Object) —

    the right hand side of the inequality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 394

def gtreq(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  case [x.type, y.type]
    when [:variable, :variable]
      equal = false
      temporary_instantiation = x.instantiate UNIQUE_VALUE
      if temporary_instantiation
        equal = y.value.value == UNIQUE_VALUE
        temporary_instantiation.remove
      end
      equal
    else
      if [x.type, y.type].include?(:variable)
        false
      else
        x >= y
      end
  end && block.call(goal) || false
end

#integer(goal, block, variable) ⇒ Boolean

Corresponds to the standard Prolog integer predicate. It is satisfied if the argument is an Integer. Use:

integer(:X)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable, Object) —

    the argument to be tested.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 156

def integer(goal, block, variable)
  variable.value.value.is_a?(Integer) && block.call(goal) || false
end

#is(goal, block, variable, *args, &is_block) ⇒ Boolean

Corresponds to the standard Prolog is predicate. It instantiates a Variable with the result of the provided block. Use:

is(:Y, :X) {|x| x + 1 }
is(:name, :first, :last) {|first, last| [first, last] }
is(:name, :first, :last) {|first, last| "#{first} #{last}" }

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable) —

    the Variable to be instantiated.

  • args (Array<Object>) —

    the arguments to be passed to the provided block.

  • is_block (Proc) —

    the block provided in the Goal’s Arguments.

Returns:

  • (Boolean) —

    whether the goal was satisfied.

Raises:



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# File 'lib/porolog/predicate/builtin.rb', line 92

def is(goal, block, variable, *args, &is_block)
  raise NonVariableError, "#{variable.inspect} is not a variable" unless variable.type == :variable
  
  result = is_block.call(*args.map(&:value).map(&:value))
  
  result && !!variable.instantiate(result) && block.call(goal) || false
end

#is_eq(goal, block, x, y) ⇒ Boolean

Corresponds to a synthesis of the standard Prolog == and is predicates. The left hand side (i.e. the first parameter) must be a variable. It compares equality if the left hand side is instantiated; otherwise, it instantiates the left hand side to the right hand side. It is satisfied if:

  • the values are equal, or

  • the variable can successfully be instantiated to the right hand side.

Use:

is_eq(:X, :Y)
is_eq(:name, ['Sam', 'Smith'])

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Porolog::Variable) —

    the left hand side of the equality / assignment.

  • y (Object) —

    the right hand side of the equality / assignment.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 207

def is_eq(goal, block, x, y)
  return false unless x.type == :variable
  return block.call(goal) if x.value.value == y.value.value
  
  !!x.instantiate(y) && block.call(goal) || false
end

#is_noteq(goal, block, variable, all_values, *exclusions) ⇒ Boolean

This does not really correspond to a standard Prolog predicate. It implements a basic constraint mechanism. The Variable is instantiated (if possible) to all possible values provide except for all exclusions. Further, the exclusions are checked for collective uniqueness. Use:

is_noteq(:digit, (0..9).to_a, :second_digit, :fifth_digit)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable) —

    the variable being instantiated.

  • all_values (Array<Object>) —

    all possible values (i.e. the domain) of the variable.

  • exclusions (Array<Object>) —

    mutually exclusive values (or variables), which the variable cannot be.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 277

def is_noteq(goal, block, variable, all_values, *exclusions)
  return false unless variable.type == :variable
  
  all_values = all_values.map(&:value).map(&:value)
  exclusions = exclusions.map(&:value).map(&:value)
  
  possible_values = goal[Porolog::anonymous]
  
  if exclusions.uniq.size == exclusions.size
    !!possible_values.instantiate(all_values - exclusions) && Predicate.call_builtin(:member, goal, block, variable, possible_values) || false
  else
    false
  end
end

#length(goal, block, list, length) ⇒ Boolean

Corresponds to the standard Prolog length predicate. It is satisfied if:

  • it is provided with an Array and an Integer where the Integer corresponds to the length of the Array,

  • it is provided with an Array and a Variable and the Variable is successfully instantiated to the length of the Array, or

  • it is provided with a Variable and an Integer where the Variable is successfully instantiated to an of anonymous variables.

Use:

length([1,2,3,4], 4)
length([1,2,3,4], :Length)
length(:L, 4)

Parameters:

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 430

def length(goal, block, list, length)
  list   = list.value.value
  length = length.value.value
  
  case [list.type, length.type]
    when [:array, :atomic]
      list.length == length
    when [:variable, :atomic]
      list.instantiate(Array.new(length){goal[Porolog::anonymous]})
    when [:array, :variable]
      length.instantiate(list.length)
    else
      false
  end && block.call(goal) || false
end

#less(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog < predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) where the first is less than the second.

Variables are not instantiated. Use:

less(:X, :Y)
less(:X, 3)
less(9, :Y)
less(:name, 'max')

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the inequality.

  • y (Object) —

    the right hand side of the inequality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 306

def less(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  if [x.type, y.type].include?(:variable)
    false
  else
    x < y
  end && block.call(goal) || false
end

#lesseq(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog <= predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) where the first is less than or equal to the second, or

  • it is provided with two uninstantiaed Variables that are bound to each other.

Variables are not instantiated (except temporarily to test if they are bound). Use:

lesseq(:X, :Y)
lesseq(:X, 3)
lesseq(9, :Y)
lesseq(:name, 'max')

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the inequality.

  • y (Object) —

    the right hand side of the inequality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 357

def lesseq(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  case [x.type, y.type]
    when [:variable, :variable]
      equal = false
      temporary_instantiation = x.instantiate UNIQUE_VALUE
      if temporary_instantiation
        equal = y.value.value == UNIQUE_VALUE
        temporary_instantiation.remove
      end
      equal
    else
      if [x.type, y.type].include?(:variable)
        false
      else
        x <= y
      end
  end && block.call(goal) || false
end

#member(goal, block, element, list, limit = 100) ⇒ Boolean

Corresponds to the standard Prolog member predicate. This implements the usual operation of member but also provides the ability to generate lists that contain the provided element, even if the element is an uninstantiated variable. Use:

member(3, [1,2,3,4,5])
member(['Chris','Smith'], [['Foo','Bar'],['Boo','Far'],['Chris','Smith']])
member(:X, [1,2,3,4,5])
member(:X, :Y)
member(:X, :Y, 5)
member(3, :Y, 10)
member(['Chris','Smith'], :Names, 16)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • element (Object) —

    the element to be found in the provided or generated list.

  • list (Array, Porolog::Variable) —

    the provided or generated list that is to contain the element.

  • limit (Integer) (defaults to: 100) —

    the number of lists to generate.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 528

def member(goal, block, element, list, limit = 100)
  element_value = element.value.value
  list          = list.value.value
  
  case [element_value.type, list.type]
    when [:atomic, :array], [:array, :array]
      satisfied = false
      list.each do |i|
        unifications = Porolog::unify(element_value, i, goal)
        if unifications
          instantiations = Porolog::instantiate_unifications(unifications)
          if instantiations
            block.call(goal) && (satisfied = true)
            instantiations.each(&:remove)
          end
        end
        
        return satisfied if goal.terminated?
      end
      satisfied
    
    when [:variable, :array]
      satisfied = false
      list.each do |i|
        instantiation = element_value.instantiate(i)
        instantiation && block.call(goal) && (satisfied = true)
        instantiation&.remove
        return satisfied if goal.terminated?
        satisfied = true
      end
      satisfied
      
    when [:variable, :variable], [:atomic, :variable], [:array, :variable]
      satisfied = false
      limit.times do |i|
        instantiation = list.instantiate([*Array.new(i){goal[Porolog::anonymous]}, element, Porolog::UNKNOWN_TAIL])
        instantiation && block.call(goal) && (satisfied = true)
        instantiation&.remove
        return satisfied if goal.terminated?
      end
      satisfied
      
    else
      false
  end
end

#nl(goal, block) ⇒ Boolean

Corresponds to the standard Prolog nl predicate. It outputs a newline. Use:

nl

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 75

def nl(goal, block)
  $stdout.puts
  block.call(goal) || false
end

#nonvar(goal, block, variable) ⇒ Boolean

Corresponds to the standard Prolog nonvar predicate. It is satisfied if the argument is not an uninstantiated variable. Use:

nonvar(:X)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable, Object) —

    the argument to be tested.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 120

def nonvar(goal, block, variable)
  variable.value.value.type != :variable && block.call(goal) || false
end

#noteq(goal, block, x, y) ⇒ Boolean

Corresponds to the standard Prolog != predicate. It is satisfied if:

  • it is provided with two values (or instantiated Variables) that are unequal, or

  • it is provided with two uninstantiaed Variables that are not bound to each other.

Variables are not instantiated; however, if they are uninstantiated, they are temporarily instantiated to a unique value to see if they are bound in some way. Use:

noteq(:X, :Y)
noteq(:name, ['Sam', 'Smith'])

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • x (Object) —

    the left hand side of the inequality.

  • y (Object) —

    the right hand side of the inequality.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 246

def noteq(goal, block, x, y)
  x = x.value.value
  y = y.value.value
  
  case [x.type, y.type]
    when [:variable, :variable]
      equal = false
      temporary_instantiation = x.instantiate UNIQUE_VALUE
      if temporary_instantiation
        equal = y.value.value == x.value.value
        temporary_instantiation.remove
      end
      !equal
    else
      x != y
  end && block.call(goal) || false
end

#permutation(goal, block, list1, list2) ⇒ Boolean

Corresponds to the standard Prolog permutation predicate. It not only returns whether one list is a permutation of the other but also can generate permutations. Use:

permutation([3,1,2,4], [1,2,3,4])
permutation([3,:A,2,4], [1,2,3,4])
permutation([3,1,2,4], [1,2,:C,4])
permutation([3,1,:B,4], [1,2,:C,4])
permutation([3,1,2,4], :Q)
permutation(:P, [1,2,3,4])

Parameters:

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 709

def permutation(goal, block, list1, list2)
  # TODO: Detect and deal with tails
  #   E.g. permutation([:H]/:T, [1,...])
  list1       = list1.value.value
  list2       = list2.value.value
  
  case [list1.type, list2.type]
    when [:array, :array]
      satisfied = false
      case [list1.variables.empty?, list2.variables.empty?]
        when [true, true]
          list1 = list1.sort_by(&:inspect)
          list2 = list2.sort_by(&:inspect)
          
          unifications   = Porolog::unify(list1, list2, goal)
          instantiations = Porolog::instantiate_unifications(unifications) if unifications
          instantiations && block.call(goal) && (satisfied = true)
          instantiations&.each(&:remove)
        
        when [false, true], [false, false]
          list2.permutation do |p|
            unifications   = Porolog::unify(list1, p, goal)
            instantiations = nil
            instantiations = Porolog::instantiate_unifications(unifications) if unifications
            instantiations && block.call(goal) && (satisfied = true)
            instantiations&.each(&:remove)
            return satisfied if goal.terminated?
          end
        
        when [true, false]
          list1.permutation do |p|
            unifications   = Porolog::unify(list2, p, goal)
            instantiations = nil
            instantiations = Porolog::instantiate_unifications(unifications) if unifications
            instantiations && block.call(goal) && (satisfied = true)
            instantiations&.each(&:remove)
            return satisfied if goal.terminated?
          end
      end
      satisfied
      
    when [:array, :variable]
      satisfied = false
      list1.permutation do |p|
        unifications   = Porolog::unify(p, list2, goal)
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
        return satisfied if goal.terminated?
      end
      satisfied
      
    when [:variable, :array]
      satisfied = false
      list2.permutation do |p|
        unifications   = Porolog::unify(list1, p, goal)
        instantiations = nil
        instantiations = Porolog::instantiate_unifications(unifications) if unifications
        instantiations && block.call(goal) && (satisfied = true)
        instantiations&.each(&:remove)
        return satisfied if goal.terminated?
      end
      satisfied
      
    else
      false
  end
end

#reverse(goal, block, list1, list2) ⇒ Boolean

Corresponds to the standard Prolog reverse predicate. It returns whether the lists are a reversal of each other, or otherwise generates a reversed list. Use:

reverse([1,2,3,4], [4,3,2,1])
reverse([1,:A,3,4], [4,3,2,1])
reverse([1,2,3,4], [4,:B,2,1])
reverse([1,:A,3,4], [4,:B,2,1])
reverse(:L, [4,3,2,1])
reverse([1,2,3,4], :L)

Parameters:

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 793

def reverse(goal, block, list1, list2)
  # TODO: Detect and deal with tails
  #   E.g. reverse([:H]/:T, [1,...])
  list1 = list1.value.value
  list2 = list2.value.value
  
  case [list1.type, list2.type]
    when [:array, :array], [:variable, :array]
      satisfied = false
      unifications   = Porolog::unify(list1, list2.reverse, goal)
      instantiations = Porolog::instantiate_unifications(unifications) if unifications
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    when [:array, :variable]
      satisfied = false
      unifications   = Porolog::unify(list1.reverse, list2, goal)
      instantiations = Porolog::instantiate_unifications(unifications) if unifications
      instantiations && block.call(goal) && (satisfied = true)
      instantiations&.each(&:remove)
      satisfied
      
    else
      false
  end
end

#ruby(goal, block, *args, &ruby_block) ⇒ Boolean

Allows a plain Ruby block to be executed as a goal. It is assumed to be successful unless evaluates to :fail . Use:

ruby(:X, :Y, :Z) {|x, y, z| csv << [x, y, z] }
ruby { $stdout.print '.' }
ruby {
  $stdout.puts 'Forcing backtracking ...'
  :fail
}

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • args (Array<Object>) —

    the arguments to be passed to the provided block.

  • ruby_block (Proc) —

    the block provided in the Goal’s Arguments.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 228

def ruby(goal, block, *args, &ruby_block)
  (ruby_block.call(goal, *args.map(&:value).map(&:value)) != :fail) && block.call(goal) || false
end

#var(goal, block, variable) ⇒ Boolean

Corresponds to the standard Prolog var predicate. It is satisfied if the argument is an uninstantiated variable. Use:

var(:X)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • variable (Porolog::Variable, Object) —

    the argument to be tested.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 108

def var(goal, block, variable)
  variable.value.value.type == :variable && block.call(goal) || false
end

#write(goal, block, *args) ⇒ Boolean

Corresponds to the standard Prolog print predicate. ‘print` could not be used because of the clash with the Ruby method. It outputs all arguments. If an argument is a variable, then if it is instantiated, its value is output; otherwise its name is output. If the value is an Array, its inspect is output instead. Use:

write('X = ', :X, ', Y = ', :Y, "\n")

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • args (Array<Object>) —

    the arguments to be passed to the provided block.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 33

def write(goal, block, *args)
  args = args.map(&:value).map(&:value)
  args = args.map{|arg|
    arg.is_a?(Array) ? arg.inspect : arg
  }
  args = args.map{|arg|
    arg.type == :variable ? arg.to_sym.inspect : arg
  }
  $stdout.print args.join
  block.call(goal) || false
end

#writenl(goal, block, *args) ⇒ Boolean

Corresponds to the standard Prolog print and nl predicate. ‘print` could not be used because of the clash with the Ruby method. It outputs all arguments and a new line. If an argument is a variable, then if it is instantiated, its value is output; otherwise its name is output. If the value is an Array, its inspect is output instead. Use:

writenl('X = ', :X, ', Y = ', :Y)

Parameters:

  • goal (Porolog::Goal) —

    the Goal to satisfy the Predicate.

  • block (Proc) —

    the continuation of solving to call if this Predicate is satisfied.

  • args (Array<Object>) —

    the arguments to be passed to the provided block.

Returns:

  • (Boolean) —

    whether the goal was satisfied.



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# File 'lib/porolog/predicate/builtin.rb', line 56

def writenl(goal, block, *args)
  args = args.map(&:value).map(&:value)
  args = args.map{|arg|
    arg.is_a?(Array) ? arg.inspect : arg
  }
  args = args.map{|arg|
    arg.type == :variable ? arg.to_sym.inspect : arg
  }
  $stdout.puts args.join
  block.call(goal) || false
end