@vesuvius: may be specific to my line of work, but you wouldn't believe the number of structured data I come across that live in some custom format, often not fully documented and "improved" over the years by successive augmentation of the original syntax. Lots of scientific instruments tend to produce this kind of junk, it seems. 

Sure, you can always write your own parsers using one of the many fine languages you mentioned, but it's a slow and pedantic job that often results in poorly maintainable code (as a reflection of the poorly defined syntax). A language - or rather, a meta-language - that allows you to clearly map the syntax would be a great help. And apparently there isn't a lot of choice in that area, especially if you expect any sort of user-friendliness or even just sanity.