Merge pull request #28 from mcr/mcr_inc_tag

increment tag

.gitignore

@@ -1,3 +1,4 @@
+*~
 *.gem
 *.swp
 pkg

lib/liquid/tags/decrement.rb

@@ -0,0 +1,39 @@
+module Liquid
+  
+  # decrement is used in a place where one needs to insert a counter
+  #     into a template, and needs the counter to survive across
+  #     multiple instantiations of the template.
+  #     NOTE: decrement is a pre-decrement, --i,
+  #           while increment is post:      i++.
+  #
+  #     (To achieve the survival, the application must keep the context)
+  #
+  #     if the variable does not exist, it is created with value 0.
+
+  #   Hello: {% decrement variable %}
+  #
+  # gives you:
+  #
+  #    Hello: -1
+  #    Hello: -2
+  #    Hello: -3
+  #
+  class Decrement < Tag
+    def initialize(tag_name, markup, tokens)      
+      @variable = markup.strip
+
+      super    
+    end    
+  
+    def render(context)
+      value = context.environments.first[@variable] ||= 0
+      value = value - 1
+      context.environments.first[@variable] = value
+      value.to_s
+    end
+  
+    private
+  end
+  
+  Template.register_tag('decrement', Decrement)
+end

lib/liquid/tags/increment.rb

@@ -0,0 +1,35 @@
+module Liquid
+  
+  # increment is used in a place where one needs to insert a counter
+  #     into a template, and needs the counter to survive across
+  #     multiple instantiations of the template.
+  #     (To achieve the survival, the application must keep the context)
+  #
+  #     if the variable does not exist, it is created with value 0.
+
+  #   Hello: {% increment variable %}
+  #
+  # gives you:
+  #
+  #    Hello: 0
+  #    Hello: 1
+  #    Hello: 2
+  #
+  class Increment < Tag
+    def initialize(tag_name, markup, tokens)      
+      @variable = markup.strip
+
+      super    
+    end    
+  
+    def render(context)
+      value = context.environments.first[@variable] ||= 0
+      context.environments.first[@variable] = value + 1
+      value.to_s
+    end
+  
+    private
+  end
+  
+  Template.register_tag('increment', Increment)
+end

test/lib/liquid/tags/inc_tag_test.rb

@@ -0,0 +1,25 @@
+require 'test_helper'
+
+
+class IncTagTest < Test::Unit::TestCase
+  include Liquid
+  
+  def test_inc
+    assert_template_result('0','{%increment port %}', {})
+    assert_template_result('0 1','{%increment port %} {%increment port%}', {})
+    assert_template_result('0 0 1 2 1',
+                           '{%increment port %} {%increment starboard%} ' +
+                           '{%increment port %} {%increment port%} ' +
+                           '{%increment starboard %}', {})
+  end
+
+  def test_dec
+    assert_template_result('9','{%decrement port %}', { 'port' => 10})
+    assert_template_result('-1 -2','{%decrement port %} {%decrement port%}', {})
+    assert_template_result('1 5 2 2 5',
+                           '{%increment port %} {%increment starboard%} ' +
+                           '{%increment port %} {%decrement port%} ' +
+                           '{%decrement starboard %}', { 'port' => 1, 'starboard' => 5 })
+  end
+
+end