Blanks are not numeric. Blanks don’t belong in a numeric field. They aren’t numeric.
 
You can use a character field as part of an expression for EVAL in order to place the result into a numeric field; but the character expression must convert to a numeric value, and blanks aren’t numeric digits. You can’t use EVAL.
 
It’s possible to use MOVE instead, but the value in the numeric field will be zero, not blanks. Blanks aren’t numeric.
 
Why would you want to do this? You should explain the problem and not ask for a specific technical solution that might not be possible. Tell us what your business objective is. What are you trying to accomplish? What business rule needs blanks in a numeric field?
 
Tom

Note that %DEC() doesn’t work. Blanks can’t give a numeric result. Blanks may be embedded within otherwise numeric characters, but there are no numeric characters in a blank field. — Tom

here is a possible way to code it.

I would probably do something like this …
Shown in free format.  But you would have to determine what to do with the On-Error Case .. I’ve set the value to zero
and turned on an error flag.

monitor;
MyDec = %Dec(MyChar)
on-error;
MyDec = 0;
MyError = *on;
endMon;