Added filters for basic arithmetic

lib/liquid/standardfilters.rb

@@ -155,6 +155,26 @@ module Liquid
       array.last if array.respond_to?(:last)
     end
     
+    # addition
+    def plus(input, operand)
+      input + operand if input.respond_to?('+')
+    end
+    
+    # subtraction
+    def minus(input, operand)
+      input - operand if input.respond_to?('-')
+    end
+    
+    # multiplication
+    def times(input, operand)
+      input * operand if input.respond_to?('*')
+    end
+    
+    # division
+    def divided_by(input, operand)
+      input / operand if input.respond_to?('/')
+    end
+    
   end
    
   Template.register_filter(StandardFilters)

test/standard_filter_test.rb

@@ -118,9 +118,25 @@ class StandardFiltersTest < Test::Unit::TestCase
     assert_template_result "a<br />\nb<br />\nc", "{{ source | newline_to_br }}", 'source' => "a\nb\nc"
   end
   
+  def test_plus
+    assert_template_result "2", "{{ 1 | plus:1 }}"
+    assert_template_result "11", "{{ '1' | plus:'1' }}"
+  end
   
+  def test_minus
+    assert_template_result "4", "{{ input | minus:operand }}", 'input' => 5, 'operand' => 1
+  end
   
+  def test_times
+    assert_template_result "12", "{{ 3 | times:4 }}"
+    assert_template_result "foofoofoofoo", "{{ 'foo' | times:4 }}"
+  end
   
+  def test_divided_by
+    assert_template_result "4", "{{ 12 | divided_by:3 }}"
+    assert_template_result "4", "{{ 14 | divided_by:3 }}"
+    assert_template_result "5", "{{ 15 | divided_by:3 }}"
+  end
   
 end