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: users-boun...@lists.ironpython.com
[mailto:users-boun...@lists.ironpython.com] 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
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