difference.rb in rdf-n3-3.1.2

- old
+ new
@@ -1,9 +1,40 @@
 module RDF::N3::Algebra::Math
   ##
   # The subject is a pair of numbers. The object is calculated by subtracting the second number of the pair from the first.
-  class Difference < SPARQL::Algebra::Operator::Binary
-    include RDF::Util::Logger
-
+  #
+  # @example
+  #     { ("8" "3") math:difference ?x} => { ?x :valueOf "8 - 3" } .
+  #     { ("8") math:difference ?x } => { ?x :valueOf "8 - (error?)" } .
+  #     { (8 3) math:difference ?x} => { ?x :valueOf "8 - 3" } .
+  #
+  # @see https://www.w3.org/TR/xpath-functions/#func-numeric-subtract
+  class Difference < RDF::N3::Algebra::ListOperator
     NAME = :mathDifference
+    URI = RDF::N3::Math.difference
+
+    ##
+    # The math:difference operator takes a pair of strings or numbers and calculates their difference.
+    #
+    # @param [RDF::N3::List] list
+    # @return [RDF::Term]
+    # @see RDF::N3::ListOperator#evaluate
+    def resolve(list)
+      list.to_a.map(&:as_number).reduce(&:-)
+    end
+
+    ##
+    # The list argument must be a pair of literals.
+    #
+    # @param [RDF::N3::List] list
+    # @return [Boolean]
+    # @see RDF::N3::ListOperator#validate
+    def validate(list)
+      if super && list.all?(&:literal?) && list.length == 2
+        true
+      else
+        log_error(NAME) {"list is not a pair of literals: #{list.to_sxp}"}
+        false
+      end
+    end
   end
 end