range function
Implementation
List<int> range({int start = 0, required int end, int step = 1}) {
assert(step != 0);
var result = <int>[];
if (step > 0) {
for (var i = start; i < end; i += step) {
result.add(i);
}
} else {
for (var i = start; i > end; i += step) {
result.add(i);
}
}
return result;
}