Render Template Collaboration

In this collaboration, we use a compiled TAL to render text.


PT – The PageTemplate

PT2 – Another PageTemplate

TI – An object that implements the TALImplementation interface.

CTAL – A compiled TAL data structure returned from a TAL compile

CTAL2 – ditto.

EEF – An object that implements the ExpressionEngineFactory interface.

EE – An object that implements the ExpressionEngine interface.

cexpr – A compiled expression. This will be context-dependent. For
example, when we are executing a define. this will be a different expression for each definition.

Sequence of calls

  • PT calls EEF.create(data)

    to create an expression engine. The expression is passed names to be included in the standard namespace. The call returns an expression engine, EE.

  • PT calls TI.renderText(CTAL, EE)

    As the TALImplementation renders the TAL, it will make calls to EE as different TAL statements are executed:

    When a node containing a define or a repeat is encountered (and a condition, if present, if true):

    • TI calls EE.beginScope()

    After processing node containing a define or a loop:

    • TI calls EE.endScope()

    when a z:define is executed:

    For each define (in order), either:

    • TI calls EE.setLocal(name, cexpr)


    • TI calls EE.setGlobal(name, cexpr)

    For each condition:

    • TI calls EE.isTrue(cexpr)

    For each repeat:

    • TI calls EE.startRepeat(name, cexpr)

    while 1:

    • TI calls EE.repeat()

      The return value is a boolean. If the value is false, we break out of the loop. Otherwise, we render the output node and continue.

    For each insert or replace:

    • TI calls EE.text(cexpr)

      To compute the text to be used. The return value is either a string, None, or an object that satisfies the DOM text-node interface.


    • TI calls EE.structure(cexpr)

      To compute the structure to be inserted. The result should be a DOM Fragment or None.

    For each attribute to be set:

    • TI calls EE.text(cexpr)

      to compute the attribute text. The result should be a string or None.

    When a use-macro is encountered,

    • TI calls EE.macro(cexpr)

      The expression engine evaluates the expression. This is likely to involve traversal into a PageTemplate, which will ask the TAL implementation for the macro.

      PT2 calls TI.findMacro(CTAL2, name)