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module SPARQL; module Algebra
class Operator
##
# The SPARQL `bound` operator.
#
# @example
# (prefix ((: <http://example.org/ns#>))
# (project (?a ?c)
# (filter (! (bound ?e))
# (leftjoin
# (bgp (triple ?a :b ?c))
# (bgp (triple ?c :d ?e))))))
#
# @see http://www.w3.org/TR/rdf-sparql-query/#func-bound
class Bound < Operator::Unary
include Evaluatable
NAME = :bound
##
# Initializes a new operator instance.
#
# @param [RDF::Query::Variable] var
# a variable
# @param [Hash{Symbol => Object}] options
# any additional options (see {Operator#initialize})
# @raise [TypeError] if any operand is invalid
def initialize(var, options = {})
super
end
##
# Returns `true` if the operand is a variable that is bound to a
# value in the given `bindings`, `false` otherwise.
#
# @param [RDF::Query::Solution] bindings
# a query solution containing zero or more variable bindings
# @param [Hash{Symbol => Object}] options ({})
# options passed from query
# @return [RDF::Literal::Boolean] `true` or `false`
# @raise [TypeError] if the operand is not a variable
def evaluate(bindings, options = {})
case var = operand
when Variable
bindings.respond_to?(:bound?) && bindings.bound?(var) ?
RDF::Literal::TRUE : RDF::Literal::FALSE
else raise TypeError, "expected an RDF::Query::Variable, but got #{var.inspect}"
end
end
end # Bound
end # Operator
end; end # SPARQL::Algebra
Version data entries
15 entries across 15 versions & 1 rubygems