Implement directives

[kumarshantanu]

Implement named directives that are handled by directive handlers. Directives should be translated after parse phase. Directive handlers act as middleware for parsed template. Directives are always at the top-level in the template--they are never nested.

macro directive

The macro directive returns a named compiled sub-template of the directive body. For the mustache template below:

{{#items}}
  {{#first}}
    <li><strong>{{name}}</strong></li>
  {{/first}}
  {{#link}}
    <li><a href="{{url}}">{{name}}</a></li>
  {{/link}}
{{/items}}

the equivalent via Basil macros would look as follows:

Definition

<#macro {:name :strong-name}><li><strong><%name%></strong></li></#macro>

<#macro {:name :url-body
         :default {:name "No-name"}}>
  <li><a href="<%url%>"><%name%></a></li>
</#macro>

Usage

<% (in items
     (in first (include strong-name))
     (in link (include url-body))) %>

Note: Macros may never nest but a macro can have <% (include another-macro) %>, which would in turn evaluate another macro and hence exhibit nesting behavior.

refer-as directive

Directives from another template can be accessed via this. Note that this works only at runtime. Another template must be referred by an alias, which is like a virtual namespace.

Definition

<#refer-as {"/libs/mylib.html" my} />

Usage

<% (include my/copyright {:date "1999-2002"}) %>

assign directive

Defines vars that are evaluated at most once every time a template is rendered. The value is memoized and reused on subsequent lookup. The var is unconditionally evaluated in the top-level env/context independent of any slots, but may be shadowed by local vars in slots when evaluating the slots.

Definition

<#assign {:foo (let [x (inc y)]
                 (+ x z))} />

Usage

<% (str "Value: " foo) %>

[kumarshantanu]

Consider the traditional extends use-case as per the links @sunng87 suggested: http://thejohnfreeman.com/blog/2012/03/23/template-inheritance-for-handlebars.html https://docs.djangoproject.com/en/1.5/topics/templates/#template-inheritance

Also consider Freemarker's inheritance model.