Class: SPARQL::Algebra::Operator Abstract

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# File 'lib/sparql/algebra/operator.rb', line 194

def self.base_uri
  @base_uri
end

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# File 'lib/sparql/algebra/operator.rb', line 204

def self.base_uri=(uri)
  @base_uri = RDF::URI(uri)
end

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# File 'lib/sparql/algebra/operator.rb', line 139

def self.evaluate(*operands)
  self.new(*operands).evaluate(RDF::Query::Solution.new)
end

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# File 'lib/sparql/algebra/operator.rb', line 70

def self.for(name, arity = nil)
  # TODO: refactor this to dynamically introspect loaded operator classes.
  case (name.to_s.downcase.to_sym rescue nil)
    when :<=>         then Compare # non-standard
    when :='         then Equal
    when :!='        then NotEqual
    when :<           then LessThan
    when :>           then GreaterThan
    when :<=          then LessThanOrEqual
    when :>=          then GreaterThanOrEqual
    when :*           then Multiply
    when :/'         then Divide
    when :+           then arity.eql?(1) ? Plus  : Add
    when :-           then arity.eql?(1) ? Minus : Subtract
    when :not, :!'   then Not
    when :plus        then Plus
    when :minus       then Minus
    when :bound       then Bound
    when :isblank     then IsBlank
    when :isiri       then IsIRI
    when :isuri       then IsIRI # alias
    when :isliteral   then IsLiteral
    when :str         then Str
    when :lang        then Lang
    when :datatype    then Datatype
    when :or, :||'   then Or
    when :and, :&&'  then And
    when :multiply    then Multiply
    when :divide      then Divide
    when :add         then Add
    when :subtract    then Subtract
    when :sameterm    then SameTerm
    when :langmatches then LangMatches
    when :regex       then Regex
    
    # Miscellaneous
    when :asc         then Asc
    when :desc        then Desc
    when :exprlist    then Exprlist

    # Datasets
    when :dataset     then Dataset
    
    # Query forms
    when :ask         then Ask
    when :base        then Base
    when :bgp         then BGP
    when :construct   then Construct
    when :describe    then Describe
    when :distinct    then Distinct
    when :filter      then Filter
    when :graph       then Graph
    when :join        then Join
    when :leftjoin    then LeftJoin
    when :order       then Order
    when :prefix      then Prefix
    when :project     then Project
    when :reduced     then Reduced
    when :slice       then Slice
    when :triple      then RDF::Query::Pattern
    when :union       then Union
    else nil # not found
  end
end

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# File 'lib/sparql/algebra/operator.rb', line 222

def self.prefixes
  @prefixes
end

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# File 'lib/sparql/algebra/operator.rb', line 232

def self.prefixes=(hash)
  @prefixes = hash
end

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# File 'lib/sparql/algebra/operator.rb', line 370

def boolean(literal)
  case literal
    when FalseClass then RDF::Literal::FALSE
    when TrueClass  then RDF::Literal::TRUE
    # If the argument is a typed literal with a datatype of
    # `xsd:boolean`, the EBV is the value of that argument.
    # However, the EBV of any literal whose type is `xsd:boolean` is
    # false if the lexical form is not valid for that datatype.
    when RDF::Literal::Boolean
      RDF::Literal(literal.valid? && literal.true?)
    # If the argument is a numeric type or a typed literal with a
    # datatype derived from a numeric type, the EBV is false if the
    # operand value is NaN or is numerically equal to zero; otherwise
    # the EBV is true.
    # However, the EBV of any literal whose type is numeric is
    # false if the lexical form is not valid for that datatype.
    when RDF::Literal::Numeric
      RDF::Literal(literal.valid? && !(literal.zero?) && !(literal.respond_to?(:nan?) && literal.nan?))
    # If the argument is a plain literal or a typed literal with a
    # datatype of `xsd:string`, the EBV is false if the operand value
    # has zero length; otherwise the EBV is true.
    else case
      when literal.is_a?(RDF::Literal) && (literal.plain? || literal.datatype.eql?(RDF::XSD.string))
        RDF::Literal(!(literal.value.empty?))
    # All other arguments, including unbound arguments, produce a type error.
      else raise TypeError, "could not coerce #{literal.inspect} to an RDF::Literal::Boolean"
    end
  end
end

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# File 'lib/sparql/algebra/operator.rb', line 295

def constant?
  !(variable?)
end

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# File 'lib/sparql/algebra/operator.rb', line 357

def eql?(other)
  other.class == self.class && other.operands == self.operands
end

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# File 'lib/sparql/algebra/operator.rb', line 276

def evaluatable?
  respond_to?(:evaluate)
end

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# File 'lib/sparql/algebra/operator.rb', line 285

def executable?
  respond_to?(:execute)
end

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# File 'lib/sparql/algebra/operator.rb', line 350

def inspect
  sprintf("#<%s:%#0x(%s)>", self.class.name, __id__, operands.map(&:inspect).join(', '))
end

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# File 'lib/sparql/algebra/operator.rb', line 254

def operand(index = 0)
  operands[index]
end

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# File 'lib/sparql/algebra/operator.rb', line 311

def optimize
  if constant?
    # Note that if evaluation results in a `TypeError` or other error,
    # we must return `self` so that the error is conserved at runtime:
    evaluate rescue self
  else
    super # returns `self`
  end
end

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# File 'lib/sparql/algebra/operator.rb', line 213

def prefixes
  Operator.prefixes
end

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# File 'lib/sparql/algebra/operator.rb', line 326

def to_sse
  operator = [self.class.const_get(:NAME)].flatten.first
  [operator, *(operands || []).map(&:to_sse)]
end

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# File 'lib/sparql/algebra/operator.rb', line 335

def to_sxp
  begin
    require 'sxp' # @see http://rubygems.org/gems/sxp
  rescue LoadError
    abort "SPARQL::Algebra::Operator#to_sxp requires the SXP gem (hint: `gem install sxp')."
  end
  require 'sparql/algebra/sxp_extensions'
  
  to_sse.to_sxp
end

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# File 'lib/sparql/algebra/operator.rb', line 264

def variable?
  operands.any? do |operand|
    operand.is_a?(Variable) ||
      (operand.respond_to?(:variable?) && operand.variable?)
  end
end