INTERACT FORUM

Windows => Plug-in Development => Topic started by: MrC on July 28, 2011, 04:29:21 pm

Title: Expression parser questions
Post by: MrC on July 28, 2011, 04:29:21 pm

Question: How is MC doing its expression parsing for the expression language?

Is there formal grammar, or stack based state machine, or ...?

Title: Re: Expression parser questions
Post by: Matt on July 28, 2011, 04:31:29 pm

I'm not certain what you're asking, but the expression parser is stack based.

This allows it to nicely handle nested expressions and parenthesis.

Evaluation of expressions runs the stack in an interpretive manner.  In other words, the stack is not compiled to machine code.

Title: Re: Expression parser questions
Post by: MrC on July 28, 2011, 05:15:32 pm

I was wondering if you had a formal grammar defined, and then used software to build your lexer/parser.

But it sounds like you've built your own.

I've been mucking about with an expression parser that would do essentially something like this:

http://ewbi.blogs.com/develops/2004/12/excel_formula_p.html  [enable javascript to use]

But I also thought about writing a formal grammar and using one of the many lexer/parser builders available.

Once an expression gets beyond a couple of nested IF statements, it becomes too cumbersome.  Finding a missing paren, or comma, can be very challenging:

http://yabb.jriver.com/interact/index.php?topic=65519.new;topicseen#new (http://yabb.jriver.com/interact/index.php?topic=65519.new;topicseen#new)

It would be ideal if MC could do some basic structured presentation of an expression for both entry and viewing (but I know you folks are busy).