Improved template syntax

*Title: Improved template syntax

*Incentive:

To make template syntax clearer and more similar to syntax of widespread
procedural programming languages.

*Documentation:

1 Variables
===========

1.1 Dollar sign
    -----------

We will use dollar sign ($) everywhere a variable is used, including assignments.
Example:
 {set $i=10}
 i: {$i}

Old-style assignments without "$" shall work.

1.2 New functions to create/destroy variables
    -----------------------------------------

We should avoid usage of {let}...{/let} block since it makes harder to
read tpl file and move code within it. Instead, two new functions
proposed: {def} and {undef}:

- def    creates a new variable in the current namespace and assigns a
         value to it. 
- undef  destroys given variable, in a manner like the corresponding PHP
         operator does. 

Syntax:
 {def $var1=<value1> [$var2=<value2> ...]}
 {undef [$var1 [$var2] ...]}

Example:
 {def $i=10 $j=20}
 {def $s1='hello' $s2='world'}
 ...
 {set $i=$i+1}
 ...
 {undef $i}
 {undef $s1 $s2}
 {undef}

If the variable being created already exists, {def} shows a warning
message and doesn't do anything except of assigning new value to the
variable. {undef} destroys all variables when called without arguments.

1.3 Variables scope
    ---------------

Variables created with {def} exist till the end of file, unless destroyed
with {undef}. A template file opens (and closes) a new scope.

2 New control structures
  ======================

A few new control structures are proposed. They are meant to be much
simplier to understand and use by developers than the allmighty
{section} function.

2.1 IF statement
    ------------

Syntax:
 {if <condition>}
 [{elseif <condition>}]
 [{else}]
 {/if}

Example:
 {if eq( $var, true() )}
 Hello world
 {else}
 No world here, move along.
 {/if}

2.2 WHILE statement
    ---------------

Syntax:
 {while <condition> [sequence <array> as $seqVar] }
 [{delimiter}...{/delimiter}]
 [{break}]
 [{continue}]
 [{skip}]
 {/while}

Example:
 {while ne( $var, false() ) }
 I like big trucks
 {/while}

2.3 DO..WHILE statement
    -------------------

Syntax:
 {do}
 [{delimiter}...{/delimiter}]
 [{break}]
 [{continue}]
 [{skip}]
 {/do while <condition> [sequence <array> as $seqVar]}

Example:
 {do}
 One more beer, please.
 {/do while eq( $drunk, false() )}

2.4 FOR statement
    -------------

Syntax:
 {for <number> to <number> as $itemVar [sequence <array> as $seqVar]}
 [{delimiter}...{/delimiter}]
 [{break}]
 [{continue}]
 [{skip}]
 {/for}

Examples:
 {for 1 to 5 as $i}
     i: {$i}
 {/for}
 {for 5 to 1 as $i}
     i: {$i}
 {/for}

$itemVar is destroyed after the loop ends.

2.5 FOREACH statement
    -----------------

Syntax:
 {foreach <array> as [$keyVar =>] $itemVar  
          [sequence <array> as $sequenceVar]
          [offset <offset>]
          [max <max>]
          [reverse]}
     [{delimiter}...{/delimiter}]
     [{break}]   
     [{continue}]
     [{skip}]
 {/foreach}

Examlple:
 {foreach $objects as $object}
 <tr>
     {foreach $object.nodes as $node sequence array(dark,light) as $class}
         <td class=$class>{$node.name|wash}</td>   
     {/foreach}
 </tr>
 {/foreach}

Variables $keyVar, $itemVar and $sequenceVar are destroyed after the loop ends. 

{foreach} does not support iterating through strings like
{section loop=...} does. So, {foreach $string as $character} will not work.

{foreach} also does not support iterating within a numeric range, like
{section loop=NUMBER} did. You should use {for} instead. 

Also, {foreach} does not use the proxy iterator as {section loop=...}
does. ie you cannot do: {$node.key}, {$node.index}.

Prameters 'offset', 'max' and 'reverse' have the same meaning as in {section}.

2.6 Notes on the loop functions
    ---------------------------

All the new loop functions support the following features: 

- 'sequence' optional parameter: array to cycle through continuously. 
- {delimiter} function: piece of code/text executed/shown after each
  iteration, except of the last one. 
- {break} function: immediately terminate the loop. 
- {continue} function: go to the next loop iteration, executing {delimiter}
  if specified. 
- {skip} function: go to the next loop iteration, without executing {delimiter}.

The {delimeter} construct must be placed as a direct child of the loop
construct. e.g. this should not be possible:

 {foreach ...}
 {if eq( $item, 5 )}
     {delimiter}----{/delimiter}
 {else}
     {delimiter}===={/delimiter}
 {/if}
 {/foreach}

Instead it must be written as:

 {foreach ...}
 {delimiter}
 {if eq( $item, 5 )}
 ----
 {else}
 ====
 {/if}
 {/delimiter}
 {/foreach}

The {skip}, {continue} and {break} functions can be used as a child no
matter how deep. In other words they will react to the last looping
construct that was in effect.

*Note* that if you have a code similar to "{section var=start loop=array(
1, 2 )}..." you cannot use $start as parameter of the new loop functions
directly, instead you should use $start.item. That is, section loop
proxy iterators must be previously dereferenced.


Online version of this article can be found here:
http://ez.no/community/developer/specs/improved_template_syntax