lispy.el demo 3: down the rabbit hole

Back to github This file in org-mode Function reference

Intro

This demo introduces the concept of edebug-less debugging.

While edebug can be great at times, I mostly like to write functions as I debug them, and edebug doesn't allow that.

Task summary

Understand how this code works: 

(setq today (org-date-to-gregorian
             (time-to-days (current-time))))

Screencast

The screencast for this demo is here: http://youtu.be/yeIzJs9oChI

Step-by-step expansion

Start with this code: 

(setq today (org-date-to-gregorian
             (time-to-days (current-time))))

step 1

Eval with e to get today's date.

step 2

  • fff or 3f (or 99f) or qd to navigate to (current-time)
  • hold e to see the value change
  • toggle C-1 to see the documentation for current-time
  • toggle C-1 off

step 3

  • h to go left once
  • e to eval. I got 735564, you might get a number larger than this.
  • toggle C-1 on/off to see what time-to-days does.

step 4

  • h to go left once
  • e to eval. I got (11 27 2014).
  • xj to jump into org-date-to-gregorian with current state, i.e. call it with 735564, the result of (time-to-days (current-time))

step 5

You should now be in org.el.

  • you can check with M-: that the value of date is 735564 (or something close)
  • to do the same thing in lispy way, you can 3mie:
    • 3m - mark third
    • i - mark inner
    • e - eval

step 6

  • qe to navigate to the first condition of the cond statement
  • e to eval it and get and get t
  • which means we can fe to get the familiar result (11 27 2014)

step 7

  • step in again with xj to end up in calendar.el
  • check if you want that date hasn't changed: 3mie
  • qe to navigate to (d0 (1- date)) statement.

step 8

  • use p to eval not (d0 (1- date)), but (setq d0 (1- date)).
  • use j to move to the next statement
  • use p again
  • use j again
  • …

step 9

By now you should have set month to 1. You need to set mdays. This can be done by navigating outward with l and pressing p. After this, all let-bound variables that should be set to nil will be set to nil.

  • navigate to the test clause of if statement with djf or qE.
  • test with e to get nil. This means that it's not New Year's eve.
  • jj to move to the else clause of if
  • e to update year
  • e to go through the while statement, you can step through it as well if you want
  • je to obtain the final result: (11 27 2014)