Ah OK. Here's a better example:
a = 10;
b = 20;
dt = New Table( "Example", Add Rows( 3 ),
New Column( char(a), Numeric, Continuous, Format( "Best", 12 ),
Set Values( [1, 2, 3] ) ),
New Column( char(b), Numeric, Continuous, Format( "Best", 12 ),
Set Values( [4, 5, 6] ) ),
);
new_expr = evalinsert(
"\[dt << New Column( "a/b", Numeric, Continuous, Format( "Best", 12 ),
Formula( :Name( "^a^" ) / :Name( "^b^" )))]\");
eval(parse(new_expr));