Fair enough. I had perhaps wrongly assumed that since Christian wanted
to figure out the type of his expression's result, he must have
differently typed database columns (or whatever) for different types of
result. Best regards all round.
Vernon Cole wrote:
Stephen said what I was trying to say. It does not matter what the
user sends you, you must try to coerce his result into something the
database will accept. This is most easily done dynamically at run time.
Also forgive my typo of "impert" for "import" ... I reread my answer
three times and still missed it.
--
Vernon Cole
On Mon, Oct 19, 2009 at 8:29 AM, Lepisto, Stephen P
<[email protected] <mailto:[email protected]>> wrote:
Jonathan,
Even if the variables going into the expression are strongly
typed, python will evaluate the expression however it can, with
the result being some type based on the coercion python applied to
each variable. However, I read Christian's problem as one where
he needed to get the value into a database and to me that was the
deciding factor as to which type to coerce the result of the
expression, regardless of the original types of the variables
going into the expression.
-----Original Message-----
From: [email protected]
<mailto:[email protected]>
[mailto:[email protected]
<mailto:[email protected]>] On Behalf Of Jonathan
Hartley
Sent: Monday, October 19, 2009 7:19 AM
To: Discussion of IronPython
Subject: Re: [IronPython] Type analysis of expression
Hey all,
Stephen, I infer that Christian can't evaluate the expression yet. (If
he could, then deriving the type of the result would be trivial)
Presumably the variables in the expression don't yet have known
values.
So he has an expression which cannot be evaluated, but he wants to
guess
what type the return value would be if the variables in the expression
were known.
The variables in the expression do have known types. So I wonder
if you
could pick a prototypical value for each variable, (eg. set all floats
to 1.0, and all integers to 1) and then evaluate the expression to see
what type the result is?
Obviously this won't work for all expressions (eg. "x / (x - 1)"), but
maybe it would work enough of the time, depending on what form your
expressions take.
Am I misunderstanding entirely, or only partially?
Jonathan
Lepisto, Stephen P wrote:
> What about treating the return type of the python expression as
object then coerce the object into the type required by the
database? If the coercion fails, then that could be treated as a
type error.
>
> For example, after using python to evaluate the expression
'2+(4*5)', the returned object could be converted to an integer
using System.Convert.ToInt32() or to a string with
System.Convert.ToString(). System.Convert throws
InvalidCastException for those cases that cannot be converted.
>
>
> -----Original Message-----
> From: [email protected]
<mailto:[email protected]>
[mailto:[email protected]
<mailto:[email protected]>] On Behalf Of Michael
Foord
> Sent: Monday, October 19, 2009 4:21 AM
> To: Discussion of IronPython
> Subject: Re: [IronPython] Type analysis of expression
>
> Christian Schmidt wrote:
>
>> Hello,
>>
>> we are using IronPython embedded into our application to
evaluate user
>> defined expression. The "variables" used in the expressions are
strongly
>> typed and the results need to be written back into a database.
>>
>> I know that the return type of a dynamic expression cannot be
determined
>> in general. But what would be a pragmatic way to guess the
return type
>> of an expression?
>>
>
> Hehe. If you're evaluating arbitrary functions provided by the
user then
> I don't know of any way of 'inferring' the return type - beyond
parsing
> it and modelling the type flow through the expression (which
would be a
> lot of work).
>
> All the best,
>
> Michael
>
>> Thanks,
>> Christian
>>
>>
>>
>> _______________________________________________
>> Users mailing list
>> [email protected] <mailto:[email protected]>
>> http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
>>
>
>
>
--
Jonathan Hartley Made of meat. http://tartley.com
[email protected] <mailto:[email protected]> +44 7737 062
225 twitter/skype: tartley
_______________________________________________
Users mailing list
[email protected] <mailto:[email protected]>
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
_______________________________________________
Users mailing list
[email protected] <mailto:[email protected]>
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
------------------------------------------------------------------------
_______________________________________________
Users mailing list
[email protected]
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
--
Jonathan Hartley Made of meat. http://tartley.com
[email protected] +44 7737 062 225 twitter/skype: tartley
_______________________________________________
Users mailing list
[email protected]
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
