Gray Soft

The programming blog of James Edward Gray II (JEG2).
  • 23


    Rich Methods

    Some APIs provide collections of dirt simple methods that just do one little thing.

    This approach in less common in Ruby though, especially in the core and standard library of the language itself. Ruby often gives us rich methods with lots of switches we can toggle and half hidden behaviors.

    Let's look at some examples of what I am talking about.

    Get a Line at a Time

    I suspect most Rubyists have used gets() to read lines of input from some kind of IO. Here's the basic usage:

    >> require "stringio"
    => true
    >> f =<<END_STR)
    => #<StringIO:0x007fd5a264fa08>
    >> f.gets
    => "<xml>\n"
    >> f.gets
    => "  <tags>Content</tags>\n"

    I didn't want to mess with external files for these trivial examples, so I just loaded StringIO from the standard library. It allows us to wrap a simple String (defined in this example using the heredoc syntax) in the IO interface. In other words, I'm calling gets() here for a String just as I could with a File or $stdin.

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  • 20


    A Curses Application

    I've now written two articles covering low-level curses and some higher abstractions. We know what curses can do at this point, but we haven't really seen how to put everything together and build a full application. Let's do that today by examining an example of moderate size.

    I have written the beginnings of a command-line Twitter client using curses. To make this easier, I developed a super simple wrapper over the raw curses API, called Rurses. Rurses, for Ruby curses, provides more Ruby-like abstractions over the clunky C API. Here's how the Twitter client looks in action:

    ┌─JEG2─────────────────────────────────┐  @
    │                                     ↑│
    │Alex Harms @onealexh… 20/03/2015 14:57│ Clayton Flesher @Cal… 19/03/2015 20:52
    │RT @postsecret:│ @TrevorBramble its inspired by, as in
    │                                      │ I played it once for about ten minutes
    │SimKlabnik 2000 @ste… 20/03/2015 14:57│ and then @JEG2 said 'go make your
    │the closure docs are finally flowing  │ version of that'.
    │from my fingertips, it seems          │
    │                                      │ Mandy Moore @theruby… 19/03/2015 18:31
    │ashe dryden @ashedry… 20/03/2015 14:57│ Thanks to @JEG2 I now want a MiP robot
    │Can anyone recommend  an interestingly│ in the worst kind of way!!!
    │written (not dry) history of Haiti?   │
    │Preferably written by a Haitian.      │ Sam Livingston-Gray … 19/03/2015 14:23
    │                                      │ @avdi @JEG2 hush! Keep this up and
    │Jessica Lord @jllord  20/03/2015 14:57│ EVERYONE WILL KNOW
    │RT @PDX44: Welcome to Portland, where │
    │the old airport carpet is dressed up  │
    │as a human and named Grand Marshal of │ Josh Susser @joshsus… 19/03/2015 14:06
    │a parade.      │ @geeksam @jeg2 @avdi POLS issue. No
    │                                      │ standard == no way to avoid surprising
    │Garann Means @garannm 20/03/2015 14:56│ many developers
    │RT @verge: Robyn launches tech        │
    │                                     ↓│                                      ↓

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  • 11


    Curses Windows, Pads, and Panels

    In the previous article, I showed how you can accomplish some terminal input and output operations using the (n)curses(w) library. What I showed for output were mostly low-level writing routines though. Included in curses are some higher level abstractions that can be used to manage your program's output. This time, I want to show some of those tools.


    The primary abstraction used in curses is the concept of a window. We actually already used them last time, but we stuck with stdscr (standard screen) which is just a window that fills the entire terminal. That's more for using curses without thinking much about windows.

    When you want them though, you can section off the terminal screen into rectangular chunks. Each chunk is a window that you can print output inside of. Here's the most basic example that I could dream up:

    require "ffi-ncurses"
      stdscr = FFI::NCurses.initscr
      window = FFI::NCurses.newwin(5, 15, 4, 2)  # make a new window
      FFI::NCurses.waddstr(window, "Hello world!")
      FFI::NCurses.wrefresh(stdscr)  # still need this

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  • 28


    Basic Curses

    In my last article, I showed off some of the various magic commands a Unix terminal recognizes and how you can use those commands to move the cursor around, change the colors of your output, and read input in a character by character fashion. It's not very common to manipulate things manually as I did in those examples. There are libraries that wrap these mechanisms and add abstractions of their own. Using one of them can be easier and less error prone.

    Probably the most famous of these higher abstraction libraries is curses. However, your version won't be called that. curses was the original library for System V UNIX. These days you are far more likely to have ncurses which a replacement library that emulates the original. The truth is, you probably don't have exactly that library either. Instead, you may have ncursesw, which is the same library with wide character (read: non-ASCII) support. Also, curses is often discussed with several add on libraries: panel, menu, and form. Documentation often covers these separate units together.

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  • 30


    Random Access Terminal

    I've recently been playing around with fancy terminal output in Ruby. I've learned quite a bit about this arcane magic. I've also realized that the documentation is pretty spotty. I want to see if I can improve that with a few blog posts, so let's dive right in.


    Program output typically happens in a linear order from top to bottom. For example, this code:

    puts "onez"
    puts "twos"
    puts "threes"

    generates this output:


    But what if you need to change some output? Could you replace the z above with an s if you needed to? Yes, but it can get a little involved.

    ANSI Escape Codes

    In many cases, we just push some characters to $stdout (the stream Kernel#puts is writing to above) and your terminal program happily shows them to the user. However, your terminal is watching these characters for special sequences that it understands. Some of those sequences of characters can cause your terminal to take actions other than just writing some output to the screen.

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  • 31


    Game Programming Patterns

    I meet a lot of programmers that tell me they got started because they wanted to build games. However, when I ask most of them which games they have built, the list rarely includes anything more than mostly unplayable toy projects.

    I can only guess at the reasons for this oddity, but I suspect it might be due to the fact that games are fairly complex. Even if you want to rebuild a fairly simple classic like Space Invaders or Snake you need to know at least a little about event loops, keyboard handling, animation, and collision detection. If your day job involves a different kind of programming, like Web application development, odds are good that you don't get a lot of practice with these concepts.

    That may not be your story, but it was definitely mine. This year I decided that it was finally time to learn how to build games. I used several sources to gain this knowledge and some helped more than others, but the biggest win by far was a book called Game Programming Patterns by Bob Nystrom.

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  • 31


    How to Avoid Taking a Dart to the Knee

    I've been playing with Dart quite a bit lately. I really enjoy the language, but there are always snags that trip up those coming from other backgrounds. Here are the top three issues that have bit me in Dart, in the hopes of saving others some pain:

    The Truth and Nothing But the Truth… Literally!

    One of the challenges of any language is figuring out what it considers to be truthy in conditional expressions. Each system has its twists, but I find Dart to be extra strict in this case.

    Here's some code illustrating the rule:

    bool isTruthy(Object condition) {
      return !!condition;
    void main() {
      var tests = [true, false, null, 42, 0, "", [ ], new Object()];
      for (var test in tests) {
        print("$test is ${isTruthy(test)}");

    That outputs:

    $ dart truthiness.dart
    true is true
    false is false
    null is false
    42 is false
    0 is false
     is false
    [] is false
    Instance of 'Object' is false

    As you can see the literal true (just that one object) is truthy in Dart and everything else is considered false. I'm in the habit of playing pretty fast and loose with truthiness from all of my time working with Ruby, so this has surprised me a few times.

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  • 24


    The Three Tick Sort

    Yesterday I showed a newer programmer some code like scores.sort_by(&:reverse). This provoked a comment about how they where going to look up sort_by() later to figure out what magic is involved here. It made me sad to realize how many cool tricks they weren't going to see in that bit of documentation.

    Allow me to enumerate those tricks for you, but first let's flesh out an example. Consider this code:

    scores = {
      fifteen:         2,
      five_card_run:   5,
      five_card_flush: 5,
      four_card_run:   4,
      four_card_flush: 4,
      his_nobs:        1,
      pair:            2,
      three_card_run:  3,
    scores.sort_by(&:reverse).each do |name, score|
      puts "Score #{score} for #{name}."
    # >> Score 1 for his_nobs.
    # >> Score 2 for fifteen.
    # >> Score 2 for pair.
    # >> Score 3 for three_card_run.
    # >> Score 4 for four_card_flush.
    # >> Score 4 for four_card_run.
    # >> Score 5 for five_card_flush.
    # >> Score 5 for five_card_run.

    In this case, the magic method call (scores.sort_by(&:reverse)) has reordered a list of Cribbage hands first by point value and then alphabetically ("ASCIIabetically" in truth). How this happens is a pretty interesting journey though.

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  • 25


    Regex Code Equivalency

    #!/usr/bin/env ruby -w
    Name = "Gray, James"
    !!(Name =~ /\AGray/)      # => true
    Name.start_with?("Gray")  # => true
    !!(Name =~ /James\z/)    # => true
    Name.end_with?("James")  # => true
    !!(Name =~ /Dana/)     # => false
    Name.include?("Dana")  # => false
    !!(Name =~ /\A\z/)  # => false
    Name.empty?         # => false
    !!(Name =~ /\AGray, James\z/)  # => true
    Name == "Gray, James"          # => true
    !!(Name =~ /\A(?:Gray, James|Gray, Dana)\z/)  # => true
    ["Gray, James", "Gray, Dana"].include?(Name)  # => true
    Name =~ /\A\w+/ && $&  # => "Gray"
    Name[/\A\w+/]          # => "Gray"
    Name =~ /\A(\w+),\s*(\w+)\z/ && $2  # => "James"
    Name[/\A(\w+),\s*(\w+)\z/, 2]       # => "James"
    Name =~ /\A(?<last>\w+),\s*(?<first>\w+)\z/ && $~[:first]  # => "James"
    Name[/\A(?<last>\w+),\s*(?<first>\w+)\z/, :first]          # => "James"
    Name.scan(/^.*\n?/)  # => ["Gray, James"]
    Name.lines           # => ["Gray, James"]
    Name.scan(/./m)  # => ["G", "r", "a", "y", ",", " ", "J", "a", "m", "e", "s"]
    Name.chars       # => ["G", "r", "a", "y", ",", " ", "J", "a", "m", "e", "s"]
    Name.gsub(/[aeiou]/, "")  # => "Gry, Jms"
    Name.delete("aeiou")      # => "Gry, Jms"
    Name.gsub(/[aeiou]/, "X") # => "GrXy, JXmXs""aeiou", "X")     # => "GrXy, JXmXs"
    # For the destructive operations that follow you can drop the `dup()` and
    # switch `sub()` to `sub!()`, as long as you don't care about the return value.
    Name.sub(/(?=,)/, " II")                 # => "Gray II, James"
    Name.dup.insert(Name.index(","), " II")  # => "Gray II, James"
    Name.sub(/\A/, "Name:  ")    # => "Name:  Gray, James"
    Name.dup.prepend("Name:  ")  # => "Name:  Gray, James"
    Name.sub(/\A.*\z/m, "Gray, Dana")  # => "Gray, Dana"
    Name.dup.replace("Gray, Dana")     # => "Gray, Dana"
    Name.sub(/\A.*\z/m, "")  # => ""
    Name.dup.clear           # => ""
    Spacey = "\tsome    space\r\n"
    Spacey.sub(/\A\s+/, "")  # => "some    space\r\n"
    Spacey.lstrip            # => "some    space\r\n"
    Spacey.sub(/\s+\z/, "")  # => "\tsome    space"
    Spacey.rstrip            # => "\tsome    space"
    Spacey.sub(/\A\s*(.+?)\s*\z/m, '\1')  # => "some    space"
    Spacey.strip                          # => "some    space"
    Spacey.sub(/(?:\r?\n|\r)\z/m, "")  # => "\tsome    space"
    Spacey.chomp                       # => "\tsome    space"
    Spacey.sub(/(?:\r\n|.)\z/m, "")  # => "\tsome    space"
    Spacey.chop                      # => "\tsome    space"
    Spacey.gsub(/ +/, " ")  # => "\tsome space\r\n"
    Spacey.squeeze(" ")     # => "\tsome space\r\n"
  • 22


    A Regex Can't Match Balanced Parentheses

    Can we do math with regular expressions?

    #!/usr/bin/env ruby -w
    def build_preparation_regex(number_regex, ops)
        (?<number>             #{number_regex}                                   ){0}
        (?<operator>           [#{}]        ){0}
        (?<term_operator_term> \g<term> \s* \g<operator> \s* \g<term>            ){0}
        (?<term>               \g<number> | \( \s* \g<term_operator_term> \s* \) ){0}
    NUMBER_REGEX               = %r{
      -?            # an optional minus
      \d+           # an integer
      (?: \. \d+)?  # an optional fractional bit
    PREPARE_MULT_AND_DIV_REGEX = build_preparation_regex(NUMBER_REGEX, %w[* /])
    PREPARE_ADD_AND_SUB_REGEX  = build_preparation_regex(NUMBER_REGEX, %w[* / + -])
    CHECK_REGEX                = %r{
      \A                   # the start of the expression
      (?<term>             # a term, which is:
        #{NUMBER_REGEX}    # a number
        |                  # or
        \( \s*             # a parenthesized group of
          \g<term>         # a term
          \s* [*/+\-] \s*  # an operator
          \g<term>         # and another term
        \s* \)             # the end of the parenthesized group
      \z                   # the end of the expression
    MATH_REGEX                 = %r{
      \( \s*
      (?<left>     #{NUMBER_REGEX} )
      (?<operator> [*/+\-]         )
      (?<right>    #{NUMBER_REGEX} )
      \s* \)
    verbose = ARGV.delete("-v")
    problem = ARGV.first.strip or abort "USAGE:  #{$PROGRAM_NAME} MATH_EXPRESSION"
    steps   = [ ]
      loop do
        steps << problem.dup if verbose
        problem.sub!(preparation) { |term| "(#{term})" } or break
    problem =~ CHECK_REGEX or abort "Error:  Invalid expression"
    solution = problem.dup
    loop do
      steps << solution.dup if verbose
      solution.sub!(MATH_REGEX) {
        $~[:left].to_f.public_send($~[:operator], $~[:right].to_f)
      } or break
    puts steps.uniq[0..-2] if verbose
    puts solution.sub(/\.0+\z/, "")

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