Once upon a time, a project I was working on had a particular sub-problem: we sucked in a data file from an external source that consisted of a collection of re

Once upon a time, a project I was working on had a particular sub-problem: we sucked in a data file from an external source that consisted of a collection of records that had to be read, validated, and either diddled around in our DB or, in the case of errors, passed off to a human for pondering. The guy who was originally assigned was quite skilled, but apparently he'd never written an interpreter before. He started with the typical Spring Beans Uber Alles infrastructure and processing for the records, but then somehow managed to get pulled off on some other aspect of the project and this part was passed on to me. After my first look at what he had, I realized that error handling, which ranged from misformatted records to nonsensical values, would be a giant ball of razor wire and lemon juice if I continued with his design. So I tossed out much of his infrastructure---keeping his good-record handling---and wrote a simple recursive descent parser that recorded errors (including their locations in the data file) for human processing. The result was simple, clean (if you've seen an interpreter before), and I haven't heard of any bugs reported in it. Turns out, IDNI.