NOT operator

spec/textquery_spec.rb

@@ -69,5 +69,17 @@ def parse(input)
     parse("a AND b OR c").eval("c").should be_false
     parse("a AND b OR c").eval("b").should be_false
   end
-
+
+  it "should accept logical NOT" do
+    %w[- NOT].each do |operator|
+      parse("#{operator} a").eval("a").should be_false
+      parse("#{operator} #{operator} a").eval("a").should be_true
+
+      parse("#{operator} a OR a").eval("a").should be_true
+      parse("a OR #{operator} a").eval("a").should be_true
+
+      parse("b AND #{operator} a").eval("b").should be_true
+      parse("b AND #{operator} a").eval("a").should be_false
+    end
+  end
 end

textquery.treetop

@@ -27,6 +27,14 @@ grammar TextQuery
     }
   end
 
+  rule unary
+    ('-' / 'NOT') {
+      def eval(a)
+        not a
+      end
+    }
+  end
+
   rule space
     [\s]*
   end
@@ -44,6 +52,12 @@ grammar TextQuery
   end
 
   rule value
+    operator:unary space value {
+      def eval(text)
+        operator.eval(value.eval(text))
+      end
+    }
+    /
     word
   end