On 1/22/12 8:30 am, Russell wrote:
> On Jan 20, 3:36 pm, TonyLanz<tolan...@gmail.com> wrote:
>> Hi all,
>> I realize this has been asked on the group before. I'm hoping someone
>> might have a "simple" workaround in IDLVM to what would be easily
>> accomplished using the execute function in IDL proper. I have a widget
>> program that contains a compound widget field that allows the user to
>> define an equation for manipulating a set of four variables. For the
>> sake of argument let's say var1, var2, var3, and var4. In this
>> compound widget field they can define what math they want to do,
>> they're restricted to addition, subtraction, multiplication and
>> division.
>>
>> so they could for example enter
>>
>> var1/var2
>> or
>> var1-var2*0.2
>> or
>> var1+var2+var3
>>
>> etc., you get the idea. Now in IDL I can just get the value from the
>> widget and simply do something like
>>
>> s='result='+cwidget_value(0)
>> status=execute(s)
>> print,result
>>
>> of course in IDLVM I'm not allowed to use EXECUTE()
>>
>> Anyone have any suggestions for implementing this simply? I know in
>> the past there was discussion of writing code to break down the string
>> and pass the pieces to the right operators or functions (using
>> call_function() ) to assemble the result.
>>
>> Tony
>
> Yes, like all things, there are several ways to skin this cat. The
> simplest way is to write the string to a file, compile that file, then
> call it as a function (and presumably delete it after you're
> finished). So if you have the command as a string, such as "result =
> var1 + var2*0.2" then just write it to a file with the appropriate
> declarations and closings. So, you'd execute:
>
> ;save the data:
> vars=[var1,var2]
>
> ;write the file:
> openw,lun,'file.pro',/get_lun
> printf,lun,'function file,vars'
> printf,lun,'return,vars(0)+vars(1)*0.2'
> printf,lun,'end'
> close,lun& free_lun,lun
>
> ;compile the file
> resolve_routine,'file.pro',/is_function
>
> ;call the function:
> result=call_function('file',var1,var2)
>
> ;clean up
> file_delete,'file.pro',/allow_non
>
>
> now the rub here is that you need to know how many variables there are
> to store in that temporary variable. Hopefully, there's some way for
> you to loop over that.
You can't compile a file from the VM, so I think you are stuck actually
parsing the expression.
> The alternative way, would be to parse the command using the usual
> order of operations rules. Then process that parsed things using pre-
> defined functions for the four arithmetic operations. Such as:
>
> t=multiply(v1,v2)
> t=divide(v1,v2)
>
> etc. WHere they have the obvious "innards". Of course, this can get
> very tedious, but is very useful. If you go down this path, I
> recommend using the byte typecasting to find the major operators:
> t=byte(cmd).
>
>
> Good Luck
> Russell
>
> PS, the reason this is so complicated, is that they don't want you
> doing this.
Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL, A Guide to Learning IDL: http://modernidl.idldev.com
Research Mathematician
Tech-X Corporation
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