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Question blocks

This is an outline for a feature currently under development for STACK 3.0.

Introduction

Question blocks are a feature that have been strongly requested to add flexibility to STACK questions by adding functional structures, i.e. conditional inclusion http://stack.maths.ed.ac.uk/live/mod/forum/discuss.php?d=153.

More maximum flexibility, blocks can be nested and conditionally evaluated. A body of CAStext is then repeatedly processed until all blocks have been interpreted into CAStext. This is currently applied to the question text and the worked solution.

General Syntax

In anticipation of unforeseen extensions, we favour a generic format inspired by the Django templating system:

{% block_type var_1 var_2 ... var_n %}
some content
{% end block_type %}

Conditional blocks

The common if statement would be written:

{% if @some_CAS_expression@ %}
The expression seems to be true
{% end if %}

An else sub-block can optionally be included:

{% if @some_CAS_expression@ %}
The expression seems to be true
{% else %}
not quite true
{% end if %}

The else if construct is also supported, e.g:

{% if @is(x=2)@ %}
   {% bold %}it is 2{% end bold %}
{% else if @is(x=3)@ %}
   it is 3
{% else %}
   {% if @is(x=4)@ %}
      {% bold %}is be 4{% end bold%}
   {% else if @is(x=5)@ %}
      it is 5
   {% else %}
      it is something else
   {% end if %}
{% end if %}

Development

Question block work is being committed to the STACK 2.1 branch http://stack.cvs.sourceforge.net/viewvc/stack/stack-dev/lib/ui/?pathrev=STACK2_1 of CVS. Current focus is on:

• Minimising number of CAS calls where possible, e.g. by evaluating all blocks at same level in one call.
• Integrating with CASText and probably lib/filters.
• Added block handling to potential response feedback.

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