}:r:     Start reader loop.
  !~>&   Push a character to the "stack".
  <:a:=- Stop reading on newline.
^:r:
@>       Rotate the newline to the end and enqueue a sentinel 0.
{~       Dequeue and rotate the first character into place.
}:p:
  ${~    Print the current character until it's 0.
^:p:
#:r:     Read again.