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Contents
module SPARQL; module Algebra
class Operator
##
# The SPARQL `lang` operator.
#
# [121] BuiltInCall ::= ... | 'LANG' '(' Expression ')'
#
# @example SPARQL Grammar
# PREFIX : <http://example/>
#
# SELECT ?x
# { ?x :p ?v .
# FILTER ( lang(?v) != '@NotALangTag@' )
# }
#
# @example SSE
# (prefix ((: <http://example/>))
# (project (?x)
# (filter (!= (lang ?v) "@NotALangTag@")
# (bgp (triple ?x :p ?v)))))
#
# @see https://www.w3.org/TR/sparql11-query/#func-lang
class Lang < Operator::Unary
include Evaluatable
NAME = :lang
##
# Returns the language tag of the operand, if it has one.
#
# If the operand has no language tag, returns `""`.
#
# @param [RDF::Literal] literal
# a literal
# @return [RDF::Literal] a simple literal
# @raise [TypeError] if the operand is not a literal
def apply(literal, **options)
case literal
when RDF::Literal then RDF::Literal(literal.language.to_s)
else raise TypeError, "expected an RDF::Literal, but got #{literal.inspect}"
end
end
##
#
# Returns a partial SPARQL grammar for this operator.
#
# @return [String]
def to_sparql(**options)
"lang(" + operands.first.to_sparql(**options) + ")"
end
end # Lang
end # Operator
end; end # SPARQL::Algebra
Version data entries
8 entries across 8 versions & 1 rubygems