csvFile:=File("test.csv");
header:=csvFile.readln().strip(); // remove trailing "\n" and leading white space
listOfLines:=csvFile.pump(List,fcn(line){ line.strip().split(",").apply("toInt") });

newFile:=File("test2.csv","w");
newFile.writeln(header + ",sum");
listOfLines.pump(newFile.writeln,fcn(ns){ String(ns.concat(","),",",ns.sum()) });
newFile.close();