I wrote a parser for IBM mainframe job control language (JCL) a decade ago. It was an interesting and infuriating excercise. I had access to several hundred job

I wrote a parser for IBM mainframe job control language (JCL) a decade ago. It was an interesting and infuriating excercise. I had access to several hundred jobs in a production batch system to validate agaisnt and the IBM online manual. When I was done I was sure I knew the code of the original and exactly how it was implemented, even having never seen it.