The slides of the conference talk at Coscup: https://coscup.org/2021/zh-TW/session/GHA7PC Content: 1. The general idea about debug 2. What is the deficiency of print when it is used for debugging? 3. tap>: a better print 4. The design philosophy of tap>

1. tap>: a simple debugging
function
Laurence Chen
Medium Blog: @replware
Clojure video tutorial
https://lambdaisland.com/

2. Agenda
● General ideas of debug
○ How most people debug
○ Scientific methods of debugging
● Problems with `print`
○ `print` conflates what to observe and how to observe
○ split the concerns
○ `tap>` is language agnostic idea

3. Many people debug like this
● Jump to the conclusion
● Change multiple things at a time, and test it
● Give up and call for help

4. Scientific method

5. Debugging tips x 1
● Reproduce the bug (Experiment)
● Change one thing at a time (Experiement)
● Read the manual and test files (Observation)

6. Debugging tips x 2
● Ask yourself “Which hypothesis will be verified by the
experiments that you plan to do?”
● As for hypothesis: combined it with rubber duck debugging
method
● Write it down

7. rubber duck debugging
● Explain every line of code to a duck
● Let the back ground process work

8. Problems with `print`
● When we need to output a time to log, which format is best?
○ timestamp
○ ISO-8601
● When certain data has 4 layers of nesting structure, how to
output it to log?

9. `print` conflates what to observe and how to observe

10. Exception handling: Doing too much

11. Exception handling: Delegate the rights to the caller

12. tap> example
● @debug
● ;;=> [(2 3 4)]
● @debug2
● ;; 2

13. Three typical ways to using tap>
● Record all the values sent in an atom --- previous code sample
● Record the last value in an atom
(def debug (atom nil))
(add-tap #(reset! debug %))
● Connect directly to different print functions
(add-tap (bound-fn* prn))

14. How to implement tap>
● A queue to hold tap values
● A dedicated thread for running all the handlers
● A mechanism to register and unregister the handler

15. tap> is a language agnostic idea

16. Reference
● Debugging with the Scientific Method --- Stuart Halloway
● Making reliable distributed systems in the presence of software
errors --- Joe Armstrong