What's the name for this type of flowchart?
charts, flowchart, visio
Solution
It's called a railroad diagram. It can more specifically be called a syntax diagram. Not sure about Visio support but other tools can get the job done: What is a good tool for creating railroad diagrams?
(source: antlr.org)
If you have a grammar file you can try to get it working in ANTLR Works, which is specifically built for working with the syntax and grammar of languages.
Problem
Take a look at this; it's very obvious how it works and what its purpose is: (source: json.org) - What's this type of chart called? - Can I make this kind of chart in Visio? - What software do you recommend for making this kind of chart?