用于先计算和后计算的工具/应用程序

Question

I am currently working on a parser and it seems that I have made a few mistakes druing the follow set calculation. So I was wondering if someone know a good tool to calculate follow and first sets so I could skip/reevaluate this error prone part of the parser construction.

Answer 1

Take a look at http://hackingoff.com/compilers/predict-first-follow-set

It's an awesome tool to compute first and follow sets in a grammar. also, you can check your answer with this visualization tools:

http://smlweb.cpsc.ucalgary.ca/start.html

Answer 2

通过将我的第一个/后续集与此网络应用程序生成的集进行比较，我发现了我的错误

Answer 3

Most parser generators that I've encountered don't have obvious means to dump this information, let alone dump it in a readable way. (I built one that does, for the reason you are suggesting, but it isn't available by itself and I doubt you want the rest of the baggage).

If your parser definition doesn't work, you mostly don't need to know these things to debug it. Staring at the rules amazingly enough helps; it also helps to build the two smallest grammar instances you can think of, one being something you expect to be accepted, and the other being a slight variant that should be rejected.

In spite of having a parser generator that will dump this information, I rarely resort to using it to debug grammars, and I've built 20-30 pretty big grammars with it.