Advanced Stepping

  When Donkey is in step mode, a number of buttons appear in the button bar  for controlling the stepping process. These buttons act on the select subexpression of the evaluation area.

• Extract
  Extract  encloses the selected subexpression in a rectangle and puts a copy of it into a new evaluation area created below. Now you can step through the subexpression separately and still see the text of the original expression. When the expression is reduced to a value, that value is placed back into the previous context, replacing the boxed original expression. You cannot extract a subexpression that is not ready for evaluation.
• Unextract
  Unextract  inserts the current evaluation area in the evaluation area from which it was previously extracted.
• Toggle Hide
  Toggle Hide   replaces the selected expression with a small, empty box. This is useful for hiding large subexpressions that get in the way when you are reading or stepping through code. To unhide an expression, select the box and push the Toggle Hide button again. Any subexpression may be hidden, and multiple subexpressions may be hidden at the same time.
• Halt Step
  Halt Step  aborts stepping, removing anything in the evaluation area of the current block. Note that the same effect is achieved by modifying the edit area of the block.