I'm attaching a simple implementation of 'while'-type task.
I needed it to perform a terminal application until it succeeds (I know it will succeed at some point) but AntContrib has no such thing so far.
My first attempt was to use nested conditions (eg. like <if> task) but it seems that Ant is evaluating such conditions only once and I was unable to make it evaluate condition at each iteration, even using <var ... unset="true"/>.
It's a quick hack and I'm sure it can be improved in many ways (eg. proper javadocs ;) ) but at least it works :)
For legal department: this code is in public domain :)