Recursive logic for parsing string into complex boolean?

问题

I'm sure this has been done before, I just can't find it.

I need to turn something like, "((A OR B) AND C) OR D" into a database query for an attribute. Specifically I'm using Ruby Sequel. Can anyone point me at an example or utility or something that will keep me from reinventing the wheel?

回答1:

You can define a grammar using ANTLR and automatically generate a Ruby parser for those type of strings. ANTLR is a parser generator and it allows you to define a grammar for a language (such as a the boolean language that you described).

After parsing, you can specify what actions need to be taken to build the desired data structure (in your case a tree data structure that captures the structure of the query).

This is not particularly a Ruby problem as ANTLR can also generate parsers for other languages. In your case it would produce a Ruby parser that you can integrate into your application to parse the strings and to produce the data structure that you need.

来源：https://stackoverflow.com/questions/12167613/recursive-logic-for-parsing-string-into-complex-boolean