It looks a bit like a tree, with all nodes not starting with ':' being terminal nodes and the other (those with a ':') being non-terminal branches.
I don't think the number of tabs is significant as you have the same information in the '(' and ')'.
I would have a look into CPAN modules which deal with trees.
Another solution might be to transform this structure into XML and then deal with it through all XML-related modules and tools.
A hand crafted XML of (part of) the above structure might read:
The trick will be to maintain a stack with the name of the tags you need to close.
"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law
In reply to Re: Logic trouble parsing a formatted text file into hashes of hashes (of hashes, etc.)