Add \s to expand to whitespace characters

lib/imbecile/regex.rb

@@ -136,6 +136,15 @@ module Imbecile
         case c
         when "d"
           CharacterRangeUnit.new("0", "9")
+        when "s"
+          ccu = CharacterClassUnit.new
+          ccu << CharacterRangeUnit.new(" ")
+          ccu << CharacterRangeUnit.new("\t")
+          ccu << CharacterRangeUnit.new("\r")
+          ccu << CharacterRangeUnit.new("\n")
+          ccu << CharacterRangeUnit.new("\f")
+          ccu << CharacterRangeUnit.new("\v")
+          ccu
         else
           CharacterRangeUnit.new(c)
         end

lib/imbecile/regex/unit.rb

@@ -98,6 +98,15 @@ module Imbecile
       def method_missing(*args)
         @units.__send__(*args)
       end
+      def <<(thing)
+        if thing.is_a?(CharacterClassUnit)
+          thing.each do |ccu_unit|
+            @units << ccu_unit
+          end
+        else
+          @units << thing
+        end
+      end
       def last_unit
         @units[-1]
       end

spec/imbecile_spec.rb

@@ -90,6 +90,19 @@ EOF
     expect(run(<<EOF, "+++")).to eq expected
 token plus \\+
 token plusplus \\+\\+
+EOF
+  end
+
+  it "lexes whitespace" do
+    expected = [
+      ["foo", "foo"],
+      ["WS", " \t"],
+      ["bar", "bar"],
+    ]
+    expect(run(<<EOF, "foo \tbar")).to eq expected
+token foo
+token bar
+token WS \\s+
 EOF
   end
 end