[seanmcdirmid]

Compare with the control flow heavy managed time [1] version:

  on widget.Mouse.Down:
  | var pw = widget.position
  | var pm = widget.Mouse.Position
  after:
  | widget.Mouse.Capture()
  | widget.position = pw + (widget.Mouse.Position - pm)
  | on widget.Mouse.Up:
  | | widget.position = widget.position # freeze widget position
  | | break                             # stop the after block so capture/dragging stops

[1] http://research.microsoft.com/pubs/211297/managedtime.pdf