Wraps first element in a channel
Wraps first element in a channel
Produce a value for the first row. If the list is empty, head does not produce any value. When the first row is deleted, the next row will be produced.
First element with the possibility of non-existence
First element with the possibility of non-existence
scala.Some with first row, or scala.None if the list is empty
Last element with the possibility of non-existence
Last element with the possibility of non-existence
scala.Some with first row, or scala.None if the list is empty
These operations obtain rows depending on absolute positions in a list