Re: Using Beanshell as an expression evaluator

Is there a reason you couldn't use your extended NameSpace object at runtime to check for any unretrieved variables?  I'm not familiar with your project's specifics, but I can't imagine any reason you couldn't do this.  Is there something your application knows at expression "compile" time it doesn't know at "run" time?

Alexey
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--- On Mon, 6/23/08, Brent Easton <[email protected]> wrote:

> From: Brent Easton <[email protected]>
> Subject: Re: [Beanshell-users] Using Beanshell as an expression  evaluator
> To: "Stewart Cambridge" <[email protected]>
> Cc: beanshell-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> Date: Monday, June 23, 2008, 6:34 AM
> Thanks Stewart,
> 
> I was aware of those, but the problem is how do you find
> out which variables are undefined and need to be set? The
> set of variables available is not canonical.
> 
> I have got something working by subclassing NameSpace with
> a custom getVariableImpl implementation that builds a list
> of undefined variables. When an expression is created, I do
> a test evaluation and record the list of undefined
> variables. When the expression is to be evaluated for real,
> I use bind the known undefined variables to the current
> property values.
> This seems to be working fine for the limited use of
> evaluating a single expression. My next task is to
> implement a more general script object. What I really need
> to work out is how to dynamically reference property values
> in my main application from within beanscript. Slowly
> getting there.
> Regards,
> Brent.
> 
> *********** REPLY SEPARATOR ***********
> 
> On 23/06/2008 at 11:21 AM Stewart Cambridge wrote:
> 
> Check the bsh.Interpreter class. The methods set(), unset()
> and eval() may help you.
> 
> 
> 
> 2008/6/22 Brent Easton <[email protected]>:
> 
> 
> I am trying to work out the best way to integrate Beanshell
> into my application. I want to use Beanshell to add the
> ability to parse and evaluate arbitrarily complex
> expressions typed in by users.
> 
> For example
> 
>  20 * xpos + ypos/2
> 
> The expressions are entered and validated at one point of
> time, but are evaluated much later, in a different phase of
> operation of the program when xpos and ypos will have
> determinable values.
> 
> I have successfully used the Parser to parse and validate
> the structure of expression.
> 
> My problem is determining and binding values to the
> variables in the expression at runtime. The variables
> 'xpos' and 'ypos' (plus a host of other
> 'variables') are not predetermined at the time the
> expression is created.
> 
> At evaluation time, I need to determine what variables are
> used in the expression are undefined, then bind them to
> values from my application, evaluate the expression and
> then return the result to my application.
> 
> Any pointers would be appreciated.
> 
> Regards,
> Brent.
> 
> 
> 
> 
> 
> 
> 
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> Brent Easton
> Analyst/Programmer
> University of Western Sydney
> Email:
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