Evaluate expression

Hello Guys!

I would like to know how to implement in smalltalk expression parser.
Something like Avi used in his DabbleDB for expressions in data cells.

In ruby i can write something like that: Sheet.eval("expression goes  
there") and
define method method_missing to parse calls to sheet cells.

Can somebody say me how to make such things work in smalltalk?

Cheers, Oleg
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> In ruby i can write something like that: Sheet.eval("expression goes
> there") and
> define method method_missing to parse calls to sheet cells.

Compiler evaluate: 'expression goes there'

> Can somebody say me how to make such things work in smalltalk?

The inspector (WAInspector) in the Halos also demonstrates it.

Don't use this for strings you receive from unknown sources through
the web. This is dangerous and people can do nasty things to your
image and machine ...

Lukas

--
Lukas Renggli
http://www.lukas-renggli.ch
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Hi Oleg,
         as Lukas said it is dangerous to evaluate any expression that a
user may enter in an input field. I can suggest two approaches that may
help you:

1. If the expressions are simple, you can use a regular expression
matcher to make sure the input matches some predefined set of valid
expressions (In VW there is the regex11 parcel).

2. Use something like SmaCC to generate a parser and "objectify" the
expression. Then you can be confident that the expression is well formed
and you can just send it a message like #eval.

HTH,
     Andrés

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On 8/23/07, Oleg Richards <[hidden email]> wrote:
> Hello Guys!
>
> I would like to know how to implement in smalltalk expression parser.
> Something like Avi used in his DabbleDB for expressions in data cells.

Actually, in Dabble DB we are very careful not to expose anything that
looks like code to the user (where code is defined as "anything that
could have a syntax error").  Expressions are built up interactively
through menus that show you the possible methods and arguments.

Cheers,
Avi
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Thanks..

I understand the way, Avi used in his DabbleDB. But there is a  
question. How did he stored expressions in his objects?
I understand that you can create them, using menus.. But what should  
be done, when i choose operation and operand in menu?
How to store it in my objects? And how to use this information later?

Cheers, Oleg
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On 8/23/07, Oleg Richards <[hidden email]> wrote:
> Thanks..
>
> I understand the way, Avi used in his DabbleDB. But there is a
> question. How did he stored expressions in his objects?
> I understand that you can create them, using menus.. But what should
> be done, when i choose operation and operand in menu?
> How to store it in my objects? And how to use this information later?

The Interpreter Pattern in the "Design Patterns" book is a good first
place to read.

Avi
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