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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?

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  • Have a look at treetop: treetop.rubyforge.org Commented Aug 29, 2012 at 7:56
  • Thanks fellas. I was basically looking for code / pseudocode that already did what I was talking about. We're only talking about three operators here, right? I'm sure its out there somewhere as this doesn't seem to be a terribly unusual thing to do. Anyway, we are in a hurry so we just bailed on parentheses for now (current customers can do without). Handling just AND and OR is no problem in a single pass. We'll revisit this later and implement parentheses. Commented Aug 30, 2012 at 13:20

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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.

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