I'll always argue against Eval(Parse())
You can just do the concat items directly with << Set Each Value (so you don't need to have the variable set)
Names default to here(1);
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
myPlatform = New Window( "Filter Col Selector Example", << modal,
fontobj = lb = Filter Col Selector( width( 250 ) ),
button box("OK", date_selection=(lb<<get selected))
);
//creating the formulacol
dt << new column("FINALNEW", character, <<SetEachValue(Concatitems( date_selection, "," ) ) );
I wonder what you're actually doing with that column if it's really a list of dates, it might be worth just putting the list into a column as an expression column type. Depending on how you're using this column.
// using an expression column
dt << new column("FINALNEW_expression", expression, <<SetEachValue(date_selection ) );