What’s in a Continuation (2016)(jlongster.com)

  1. Write some JS code in chrome and verify expected behaviour.
  2. Add a debugger statement.
  3. When the debugger pops up, go down a few frames and add debug point.
  4. Right click the frame and select restart.
  5. In the new break point, write some code in the console to modify the state.
  6. When you step through the code, it now does something else.

  This is the TXR Lisp interactive listener of TXR 181.
  Quit with :quit or Ctrl-D on empty line. Ctrl-X ? for cheatsheet.
  1> (defun yflatten (obj)
       (labels ((flatten-rec (obj)
                  (cond
                    ((null obj))
                    ((atom obj) (yield-from yflatten obj))
                    (t (flatten-rec (car obj))
                       (flatten-rec (cdr obj))))))
         (flatten-rec obj)
         nil))
  yflatten
  2> (yflatten '(1 (2 3 (4) . 5) 6))
  #S(sys:yld-item val 1 cont #<intrinsic fun: 1 param>)

  3> (obtain (yflatten '(1 (2 3 (4) . 5) 6)))
  #<interpreted fun: lambda (: resume-val)>
  4> [*3]
  1
  5> [*3]
  2
  6> [*3]
  3
  7> [*3]
  4
  8> [*3]
  5
  9> [*3]
  6
  10> [*3]
  nil
  11> [*3]
  nil

  (defun flatten-rec (obj)
    (cond
      ((null obj))
      ((atom obj) (yield-from yflatten obj))
      (t (flatten-rec (car obj))
         (flatten-rec (cdr obj)))))
  
  (defun yflatten (obj)
    (flatten-rec obj)
    nil)

  1> (trace yflatten flatten-rec)
  nil
  2> (obtain (yflatten '(1 (2 3 (4) . 5) 6)))
  #<interpreted fun: lambda (: resume-val)>
  3> [*2]
  (yflatten ((1 (2 3 (4) . 5) 6))
    (flatten-rec ((1 (2 3 (4) . 5) 6))
      (flatten-rec (1)
    #S(sys:yld-item val 1 cont #<intrinsic fun: 1 param>))
  1
  4> [*2]
        nil)
      (flatten-rec (((2 3 (4) . 5) 6))
        (flatten-rec ((2 3 (4) . 5))
          (flatten-rec (2)
  2
  5> [*2]
            nil)
          (flatten-rec ((3 (4) . 5))
            (flatten-rec (3)
  3
  6> [*2]
              nil)
            (flatten-rec (((4) . 5))
              (flatten-rec ((4))
                (flatten-rec (4)
  4
  7> [*2]
                  nil)
                (flatten-rec (nil)
                  t)
                t)
              (flatten-rec (5)
  5
  8> [*2]
                nil)
              nil)
            nil)
          nil)
        (flatten-rec ((6))
          (flatten-rec (6)
  6
  9> [*2]
            nil)
          (flatten-rec (nil)
            t)
          t)
        t)
      t)
  nil

  10> [*2]
            nil)
          (flatten-rec (nil)
            t)
          t)
        t)
      t)
  nil
  11> [*2]
            nil)
          (flatten-rec (nil)
            t)
          t)
        t)
      t)
  nil