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module SPARQL; module Algebra
class Operator
##
# The SPARQL `isBlank` operator.
#
# @example
# (prefix ((xsd: <http://www.w3.org/2001/XMLSchema#>)
# (: <http://example.org/things#>))
# (project (?x ?v)
# (filter (isBlank ?v)
# (bgp (triple ?x :p ?v)))))
#
# @see http://www.w3.org/TR/rdf-sparql-query/#func-isBlank
class IsBlank < Operator::Unary
include Evaluatable
NAME = :isBlank
##
# Returns `true` if the operand is an `RDF::Node`, `false` otherwise.
#
# @param [RDF::Term] term
# an RDF term
# @return [RDF::Literal::Boolean] `true` or `false`
# @raise [TypeError] if the operand is not an RDF term
def apply(term)
case term
when RDF::Node then RDF::Literal::TRUE
when RDF::Term then RDF::Literal::FALSE
else raise TypeError, "expected an RDF::Term, but got #{term.inspect}"
end
end
end # IsBlank
end # Operator
end; end # SPARQL::Algebra
Version data entries
31 entries across 31 versions & 1 rubygems