Many moons ago, when Propel 1.2 was its most recent incarnation, I wrote a web-based program to convert simple bracketed WHERE clauses to equivalent Criteria statements in PHP. This works recursively to parse an expression and stores the resultant tree in a nested system of classes. The system is now of limited usefulness, since Propel’s recommended syntax has moved on to a different syntax, but it may still be of interest, and could probably be used to bring the output syntax up to date!

Here’s the web app, its source code, and a related discussion thread.