class RDF::N3::Algebra::ListOperator

This is a generic operator where the subject is a list or binds to a list and the object is either a constant that equals the evaluation of the subject, or a variable to which the result is bound in a solution

Constants

NAME

Public Instance Methods

as_literal(object) click to toggle source

Returns a literal for the numeric argument.

# File lib/rdf/n3/algebra/list_operator.rb, line 85
def as_literal(object)
  case object
  when Float
    literal = RDF::Literal(object, canonicalize: true)
    literal.instance_variable_set(:@string, literal.to_s.downcase)
    literal
  else
    RDF::Literal(object, canonicalize: true)
  end
end
execute(queryable, solutions:, **options) click to toggle source

The operator takes a list and provides a mechanism for subclasses to operate over (and validate) that list argument.

@param [RDF::Queryable] queryable

the graph or repository to query

@param [RDF::Query::Solutions] solutions

solutions for chained queries

@return [RDF::Query::Solutions]

# File lib/rdf/n3/algebra/list_operator.rb, line 19
def execute(queryable, solutions:, **options)
  RDF::Query::Solutions(solutions.map do |solution|
    # Might be a variable or node evaluating to a list in queryable, or might be a list with variables
    subject = operand(0).evaluate(solution.bindings, formulae: formulae)
    next unless subject
    # If it evaluated to a BNode, re-expand as a list
    subject = RDF::N3::List.try_list(subject, queryable).evaluate(solution.bindings, formulae: formulae)
    object = operand(1).evaluate(solution.bindings, formulae: formulae) || operand(1)
    object = formulae.fetch(object, object) if object.node?

    log_info(self.class.const_get(:NAME), "subject") {SXP::Generator.string(subject.to_sxp_bin).strip}
    log_info(self.class.const_get(:NAME), "object") {SXP::Generator.string(object.to_sxp_bin).strip}
    next unless validate(subject)

    lhs = resolve(subject)
    if lhs.nil?
      log_error(self.class.const_get(:NAME), "subject evaluates to null") {subject.inspect}
      next
    end

    if object.variable?
      log_debug(self.class.const_get(:NAME), "result") {SXP::Generator.string(lhs.to_sxp_bin).strip}
      solution.merge(object.to_sym => lhs)
    elsif object != lhs
      log_debug(self.class.const_get(:NAME), "result: false")
      nil
    else
      log_debug(self.class.const_get(:NAME), "result: true")
      solution
    end
  end.compact.uniq)
end
input_operand() click to toggle source

Input is generically the subject

@return [RDF::Term]

# File lib/rdf/n3/algebra/list_operator.rb, line 56
def input_operand
  operand(0)
end
resolve(list) click to toggle source

Subclasses implement ‘resolve`.

@param [RDF::N3::List] list @return [RDF::Term]

# File lib/rdf/n3/algebra/list_operator.rb, line 65
def resolve(list)
  raise NotImplemented
end
validate(list) click to toggle source

Subclasses may override or supplement validate to perform validation on the list subject

@param [RDF::N3::List] list @return [Boolean]

# File lib/rdf/n3/algebra/list_operator.rb, line 74
def validate(list)
  if list.list? && list.valid?
    true
  else
    log_error(NAME) {"operand is not a list: #{list.to_sxp}"}
    false
  end
end