b:loop

The b:loop tag, or the loop tag, is a tag for iterating across a range of values and repeating the descendants of the b:loop tag for each iteration.

Attributes

values - Values to iterate across. This can be an expression for a data array, e.g. data:posts, or it can be a specific number range, e.g. '1 to 12'.
var - Name of the variable which will hold the current value.
index - Name of the variable which will hold the index of the current iteration.
reverse - Boolean value for whether to iterate the values backward.

Example usage

A defined array

The following example emits the post title and body for each of the posts in the data:posts dictionary.
<b:loop var='post' values='data:posts' index='i'>
  <div>
    <h3>
      <b:eval expr='data:i + 1' />. <data:post.title />
    </h3>
    <div>
      <data:post.body />
    </div>
  </div>
</b:loop>

Example output might be:
<div>
  <h3>
    1. Second post ever
  </h3>
  <div>
    This is the second post.
  </div>
</div>
<div>
  <h3>
    2. Hello world
  </h3>
  <div>
    This is my first post, ever!
  </div>
</div>

An arbitrary iteration

In another example, we produce a list of labels searches, by iterating across an inline-defined set of labels and producing links for searching for that label. 
<ul>
  <b:loop var='label'
          values='["cat", "dog", "mouse", "hyena"]'>
    <li b:whitespace='remove'>
      <a href='data:blog.searchUrl params { label: data:label }' b:whitespace='remove'>
        <data:label />
      </a>
    </li>
  </b:loop>
</ul>

The resulting output, for myblog.blogspot.com, would be the following list.
<ul>
  <li><a href='http://myblog.blogspot.com/search?label=cat'>cat</a>
  <li><a href='http://myblog.blogspot.com/search?label=dog'>dog</a>
  <li><a href='http://myblog.blogspot.com/search?label=mouse'>mouse</a>
  <li><a href='http://myblog.blogspot.com/search?label=hyena'>hyena</a>
</ul>

Tracking the index

In this example, we flag the last item in the list with the class 'last'.

<b:loop var='post' values='data:posts' index='i'>
  <div>
    <b:class name='last' cond='data:i == data:posts.size + 1' />
    <h3><data:post.title /></h3>
    <div>
      <data:post.body />
    </div>
  </div>
</b:loop>

Note that the index attribute is the zero-based offset into the loop.