Notes on Our First Project

Setting up the dictionary project as an actual separate Elixir project is a more structured approach than I’ve seen so far. Use of multiple projects has been previously discussed but examples to date have been more at the module level within a project. Excited to see this approach introduced so early in the course. Already changing my assumptions about future project construction.

Also new to me was the use of @ to run a function at compile time. I have used @ notation, but only to declare a fixed value. Not sure when I would use a dynamic compile-time value vs. a configuration, but good to know it exists.

Notes

• Link to the Our First Project repository.
• Course uses Elixir 1.12.3. I’m using Elixir 1.14.2.
• Set up .iex.exs to match recommendation.
• In IEx:
  • h IO shows module-level documentation.
  • h IO. shows functions in the module.
• Commandline editing uses EMACS keys.
• v evaluates that line number.
  • can be used in expressions:

    v(1) * 22
    

• iex:break takes you to top-level of the REPL.
• mix new xxx examples not showing a ./config directory. The last book always expected that to be created.
• mix run -e Dictionary.hello
• Loading new code:
  • Compile the file: c "lib/dictionary.ex"
  • Recompile the module: r Dictionary

Exercises

Bind the string “had we but world enough, and time” to a variable.

Use functions from the String module to:

• Split it into two parts: the stuff before and the stuff after the comma.
• Split it into a list of characters, where each entry in the list is a single character string.
• Split it into a list of characters, where each entry in the list is the integer representation of that character.1
• reverse the string (hmmm… the first two words of the result are interesting)

  iex(1)> world_enough = "had we but world enough, and time"
  "had we but world enough, and time"
  
  iex(2)> String.split(world_enough, ~r/,/)
  ["had we but world enough", " and time"]
  
  # The following could have used String.codepoints.
  iex(3)> String.split(world_enough, ~r/.{1}/, include_captures: true, trim: true)
  ["h", "a", "d", " ", "w", "e", " ", "b", "u", "t", " ", "w", "o", "r", "l", "d",
   " ", "e", "n", "o", "u", "g", "h", ",", " ", "a", "n", "d", " ", "t", "i", "m",
   "e"]
  
  iex(4)> String.to_charlist(world_enough)
  
  iex(5)> String.reverse(world_enough)
  "emit dna ,hguone dlrow tub ew dah"
  
  # Does not explicitly state, but I'm assuming this is the Myers Difference.
  iex(6)> bacon_enough = "had we but bacon enough, and treacle"
  "had we but bacon enough, and treacle"
  
  iex(7)> String.myers_difference(world_enough, bacon_enough)
  [
    eq: "had we but ",
    del: "w",
    ins: "bac",
    eq: "o",
    del: "rld",
    ins: "n",
    eq: " enough, and t",
    del: "im",
    ins: "r",
    eq: "e",
    ins: "acle"
  ]

Review Questions

1. Letters sorted into alphabetical order in “conventional” language.

   # Elixir
   iex(1)> "bobby jones" |> String.codepoints() |> Enum.sort() |> Enum.join()
   " bbbejnoosy"

   # Python
   "".join(sorted([*"bobby jones"]))

2. Some lines of conventional code translated to Elixir.

   # join(sort(split(word)))
    iex(1)> "bobby jones" |> String.codepoints() |> Enum.sort() |> Enum.join()
    " bbbejnoosy"
   
    # length(split(wordlist, /\n/))
    iex(2)> "bobby jones\nsuzie queue" |> String.split("\n") |> length
    2
   
    # join(split(string, "\t"), ",")
    iex(3)> "tabbed\twords" |> String.split("\t") |> Enum.join(",")
    "tabbed,words"
   
   ' bbbejnoosy'

All notes and comments are my own opinion. Follow me at @rgacote@genserver.social