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Lesson Goals

  • [ ] destructuring
  • [ ] sequences, lazy seqs
  • [ ] lexical vs dynamic scoping
  • [ ] reduce, functional idioms

Preparatory Material for Lesson 2

Lesson goals: To further our study of the basics of the clojure language, deepen our familiarity with our tools, and get some practice looking around and writing some code ourself.

  • Read chapters 4 and 5, and appendix A, of Brave and True
  • Do koans from files 1-> 9, 11, 12, 15
  • WRITE DOWN any questions you have!!! We will reserve time to go over questions at the beginning of the lecture
  • Practice finding reference material:
    • “Show docstring of function” [C-c C-d d] in emacs, in VS Code, just hover point over the symbol
    • look at the clojure cheat sheet: https://clojure.org/api/cheatsheet Try to get a feel for the functions available to manipulate the immutable values we discussed. Pay particular attention to the functions which manipulate maps. Practice many of these functions to intuitively see what they do; e.g you find an interesting function in the cheatsheet called assoc-in. You see that it has a signature of the form: [m [k & ks] v]. Remember that m stands for map, k for key, v for value. You try it! 
      (assoc-in {:foo 8} [:a :b :c] 99)
;; =>  {:foo 8, :a {:b {:c 99}}}

      Think about when such a function might be useful. Why does it exist? Why did the designers add it to the language?

      Alan Perlis once wrote:

      It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures. —Alan Perlis

      What do you think he meant? Can you relate this quote to Object oriented programming vs. the sort of functional programming you’re learning now?

  • Jump to function definitions you don’t understand. Don’t worry if you can’t understand their implementation yet; LOOK at the style and structure of how the code is written. Can you figure out what all the parts are trying to do? Look at the definitions of such basic functions as complement, constantly, identity. Could you have written such functions? Can you guess why they exist?
  • Practice structural code editing (i.e. paredit mode in emacs) In VS Code, right click the mouse and choose the “Command Palette” menu entry, then restrict the search to those commands which match the string “paredit”. Pay particular attention to and memorize the keybindings of the following commands until they become natural:
    • [C-M-f] paredit-forward
    • [C-M-b] paredit-backward
    • [C-M-u] paredit-backward-up
    • [C-M-p] paredit-backward-down
    • [C-M-n] paredit-forward-up
    • [C-M-d] paredit-forward-down
    • [C-M-k] kill-sexp

    Study as many of the others as time allows to at least be aware of their existence, even if you don’t remember their names or keybindings at this point.

  • For those feeling brave, try to write a function which solves this problem: http://www.4clojure.com/problem/77 I will provide my solution to compare with you at the next lecture.

See you all soon!