Can Eval evaluate a date arithmetic expression?

[Penguin]

For some odd reason, I am trying to do some complex time calculations
that I want to let the user define. So I set up a table with

EventID EventType EventExpression
1 SolarNoon datediff("n",Sunrise,Sunset)
etc.

This is supposed to be evaluated with
TimeofNoon=Eval(EventExpression)

Unfortunately, it keeps telling me it doesn't recognize Sunrise,
whether it's a control on the form, or a publicly declared variable,
or part of a publicly declared class.
I also tried using single quotes in the expression to be evaluated.
I also tried enclosing the eval in another layer:
Function EvaluateExpression(stExpression As String)
EvaluateExpression = Eval(stExpression)
End Function
Of course, if I go to debug and do
?stExpression
and then put a ? in front of the result, it works just fine!

I could just forget all this and use case statements. However, I
wanted to leave room for a user to add some calculation that didn't
occur to me. Can it be done?

[Steve Jorgensen]

Eval has no idea about anything on a form unless yuo tell it which form, so
you should be able to change the expression to
datediff("n",[Forms]![frmMyForm]![Sunrise],[Forms]![frmMyForm]![Sunset]). If
you want to use an expression from code, Eval can see public functions, but
not variables, so you would have to create a function that returns the value
from the variable.

On 28 Nov 2004 23:11:26 -0800, pe***********@aol.com (Penguin) wrote:

For some odd reason, I am trying to do some complex time calculations
that I want to let the user define. So I set up a table with

EventID EventType EventExpression
1 SolarNoon datediff("n",Sunrise,Sunset)
etc.

This is supposed to be evaluated with
TimeofNoon=Eval(EventExpression)

Unfortunately, it keeps telling me it doesn't recognize Sunrise,
whether it's a control on the form, or a publicly declared variable,
or part of a publicly declared class.
I also tried using single quotes in the expression to be evaluated.
I also tried enclosing the eval in another layer:
Function EvaluateExpression(stExpression As String)
EvaluateExpression = Eval(stExpression)
End Function
Of course, if I go to debug and do
?stExpression
and then put a ? in front of the result, it works just fine!

I could just forget all this and use case statements. However, I
wanted to leave room for a user to add some calculation that didn't
occur to me. Can it be done?