(Nth) Alternative syntax proposal for FreeMarker

This has been raised several times already, especially from people  
coming from Velocity-land... The FreeMarker syntax is quite heavy.  
Now we can use square brackets which help when working with XML/HTML  
templates but there is still room for improvement.

My suggestion is quite simple, but it may require a new parser.

Comparison:

Directive without a body
--------------------------------
=FreeMarker classic=

Opening: <#directive
Closing: />

=FreeMarker 'light'=

Opening: ##directive
Closing: end of line


Directive with a body
----------------------------
=FreeMarker classic=

Opening: <#directive parameters>
Closing: <#/directive> (short form: <#/>)

=FreeMarker 'light'=

Opening: ##directive parameters
Closing: ##/directive (short form: ##/)


Macro call without a body
----------------------------------
=FreeMarker classic=

Opening: <@macroname
Closing: />

=FreeMarker 'light'=

Opening: @@macroname
Closing: end of line


Macro call with a body
------------------------------
=FreeMarker classic=

Opening: <@macroname parameters>
Closing: </@macroname> (short form: <@/>)

=FreeMarker 'light'=

Opening: ##@macroname parameters
Closing: ##/@macroname (short form: ##/)


Single-line comment
----------------------------
=FreeMarker classic=

Opening: <#-- comment
Closing: -->

=FreeMarker 'light'=

Opening: ##-- comment
Closing: end of line


Multi-line comment
--------------------------
=FreeMarker classic=

Opening: <#--
Closing: -->

=FreeMarker 'light'=

Opening: ##--
Closing: ##/-- (short form: ##/)


I chose double characters to minimize clashes with the rendered  
document. Escaping is done by trippling the double character, ie. ###  
renders as ## and @@@ renders as @@. Using single characters would  
require a different escaping rule.

To put more than one directive in a line, enclose in brackets eg. ## 
(if n > 5)##(-- display in long form)@@(showLongList items)##(else)@@ 
(showList items)##/

I tried it on a few templates and I think the result is quite pleasing.
Now a real-world example (borrowed from http://www.devdaily.com/java/ 
jwarehouse/spring-framework-2.5.3/dist/resources/spring.ftl.shtml)

Original
-----------

<#--
  * formCheckboxes
  *
  * Show checkboxes.
  *
  * @param path the name of the field to bind to
  * @param options a map (value=label) of all the available options
  * @param separator the html tag or other character list that should  
be used to
  *    separate each option. Typically ' ' or '<br>'
  * @param attributes any additional attributes for the element (such  
as class
  *    or CSS styles or size
-->
<#macro formCheckboxes path options separator attributes="">
     <@bind path/>
     <#list options?keys as value>
         <#assign id="${status.expression}${value_index}">
        <#assign isSelected = contains(status.value?default([""]),  
value)>
        <input type="checkbox" id="${id}" name="${status.expression}"  
value="${value?html}"<#if isSelected> checked="checked"<#/if> $ 
{attributes}<@closeTag/>
         <label for="${id}">${options[value]?html}${separator}
     </#list>
     <input type="hidden" name="_${status.expression}" value="on"/>
</#macro>

<#--
  * showErrors
  *
  * Show validation errors for the currently bound field, with
  * optional style attributes.
  *
  * @param separator the html tag or other character list that should  
be used to
  *    separate each option. Typically '<br>'.
  * @param classOrStyle either the name of a CSS class element (which  
is defined in
  *    the template or an external CSS file) or an inline style. If  
the value passed in here
  *    contains a colon (:) then a 'style=' attribute will be used,  
else a 'class=' attribute
  *    will be used.
-->
<#macro showErrors separator classOrStyle="">
     <#list status.errorMessages as error>
         <#if classOrStyle == "">
             <b>${error}
         <#else>
             <#if classOrStyle?index_of(":") == -1><#assign  
attr="class"><#else><#assign attr="style"></#if>
             <span ${attr}="${classOrStyle}">${error}
         </#if>
         <#if error_has_next>${separator}
     </#list>
</#macro>

<#--
  * checkSelected
  *
  * Check a value in a list to see if it is the currently selected  
value.
  * If so, add the 'selected="selected"' text to the output.
  * Handles values of numeric and string types.
  * This function is used internally but can be accessed by user code  
if required.
  *
  * @param value the current value in a list iteration
-->
<#macro checkSelected value>
     <#if stringStatusValue?is_number && stringStatusValue == value? 
number>selected="selected"</#if>
     <#if stringStatusValue?is_string && stringStatusValue ==  
value>selected="selected"</#if>
</#macro>

<#--
  * closeTag
  *
  * Simple macro to close an HTML tag that has no body with '>' or '/>',
  * depending on the value of a 'xhtmlCompliant' variable in the  
namespace
  * of this library.
-->
<#macro closeTag>
     <#if xhtmlCompliant?exists && xhtmlCompliant>/><#else>></#if>
</#macro>


'Light' version
------------------

##--
  * formCheckboxes
  *
  * Show checkboxes.
  *
  * @param path the name of the field to bind to
  * @param options a map (value=label) of all the available options
  * @param separator the html tag or other character list that should  
be used to
  *    separate each option. Typically ' ' or '<br>'
  * @param attributes any additional attributes for the element (such  
as class
  *    or CSS styles or size
  ##/
##macro formCheckboxes path options separator attributes=""
     @@bind path
     ##list options?keys as value
         ##assign id="${status.expression}${value_index}"
         ##assign isSelected = contains(status.value?default([""]),  
value)
         <input type="checkbox" id="${id}" name="$ 
{status.expression}" value="${value?html}"##(if isSelected)  
checked="checked"##(/if) ${attributes}@@closeTag
         <label for="${id}">${options[value]?html}${separator}
     ##/list
     <input type="hidden" name="_${status.expression}" value="on"/>
##/macro

##--
  * showErrors
  *
  * Show validation errors for the currently bound field, with
  * optional style attributes.
  *
  * @param separator the html tag or other character list that should  
be used to
  *    separate each option. Typically '<br>'.
  * @param classOrStyle either the name of a CSS class element (which  
is defined in
  *    the template or an external CSS file) or an inline style. If  
the value passed in here
  *    contains a colon (:) then a 'style=' attribute will be used,  
else a 'class=' attribute
  *    will be used.
  ##/
##macro showErrors separator classOrStyle=""
     ##list status.errorMessages as error
         ##if classOrStyle == ""
             <b>${error}
         ##else
             ##(if classOrStyle?index_of(":") == -1)##(assign  
attr="class")##(else)##(assign attr="style")##/
             <span ${attr}="${classOrStyle}">${error}
         ##/if
         ##(if error_has_next)${separator}##/
     ##/list
##/macro

##--
  * checkSelected
  *
  * Check a value in a list to see if it is the currently selected  
value.
  * If so, add the 'selected="selected"' text to the output.
  * Handles values of numeric and string types.
  * This function is used internally but can be accessed by user code  
if required.
  *
  * @param value the current value in a list iteration
  ##/
##macro checkSelected value
     ##(if stringStatusValue?is_number && stringStatusValue == value? 
number)selected="selected"##/
     ##(if stringStatusValue?is_string && stringStatusValue == value) 
selected="selected"##/
##/macro

##--
  * closeTag
  *
  * Simple macro to close an HTML tag that has no body with '>' or '/>',
  * depending on the value of a 'xhtmlCompliant' variable in the  
namespace
  * of this library.
  ##/
##macro closeTag
     ##(if xhtmlCompliant?exists && xhtmlCompliant)/>##(else)>##/
##/macro


For reference, the first macro in case FreeMarker 'light' uses single  
characters would look like:

#macro formCheckboxes path options separator attributes=""
     @bind path
     #list options?keys as value
         #assign id="${status.expression}${value_index}"
         #assign isSelected = contains(status.value?default([""]),  
value)
         <input type="checkbox" id="${id}" name="$ 
{status.expression}" value="${value?html}"#(if isSelected)  
checked="checked"#(/if) ${attributes}@closeTag
         <label for="${id}">${options[value]?html}${separator}
     #/list
     <input type="hidden" name="_${status.expression}" value="on"/>
#/macro


What do you think?
-- Denis.

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