[Gambas-user] Custom Eval (was Re: The new Border class)

[Benoît Minisini]

Le 05/01/2015 21:46, Fabien Bodard a écrit :
>> What do you mean?
>>
>> --
>> Benoît Minisini
>
> I think about a tool that will be able to interpret inline formulas
> like in a spreedsheet.
>
> i have done something like that for playing myself but i'm not a
> specialist of interpreters like you.
>
> for example :
>
> =Myvar1 + 3 *(3*myvar2)
> =MYFUNCTION(myvar1; myvar2) + MyVar3
>
> the function can be initialised for example like
>
> Interpret.Function.Add("MYFunction", nbreArgs, typeRetVal)
>
> And will call Public Sub Interpret_MyFunction(Arg1 as variant, arg2 as
> variant,...) as variant
>
> A Special Event will query the vars values : Public Sub
> Interpret_GetVar(sVarName as string) as Variant
>
> All the stuff of the interpreter will be to manage conditionnal
> requirement and calculate values  or concatenate strings. So this tool
> will be usefull for user level programmation.
> Like in spreadsheet or in reports formulas. It can be extended near to
> unlimited. Some functions can be hardcoded like mathematical ones.
> Others are depend of the context so must be implemented for each
> widget or component. It's not the fastest way to make compute but the
> most flexible.
>
> I hope my english is not inapprehensible
>

If I understand well, you need some sort of custom Eval().

More precisely, I think what you need is a Gambas hook inside the reader 
part of Eval() (the first part of its internal compiler) where you tell 
how to translate any symbol into a Gambas function or a call to a method 
into one of your classes, everything else being forbidden.

That way, you keep the Gambas syntax, except that all function names are 
redefined, and every interpreter class is forbidden except the one you 
allow explicitly.

Just an idea...

-- 
Benoît Minisini