The Perl 6 Implementation of Hangman

examples/games/hangman.p6

1. magical lexicals
2. ternary operator
3. err and //
4. unary =
5. smart matching
6. junctions
7. for and loop
8. string concatenation
9. grep and adverbial blocks
10. constants
11. interpolating function results into strings
12. the new repeat operatator

sub cls - ternary operator, magical lexicals

sub cls returns Void {
    system(($?OS eq any<MSWin32 mingw cygwin>) ?? 'cls' :: 'clear');
}

    

• Returns nothing.
• Checks the magical lexical (S02) $?OS against a junction consisting of 3 values.
• The angle bracket syntax is a shorthand for qw(space sep wds) in Perl 5 and q:w/space sep words/ in Perl 6. See S02 for more details
• The ternary operator ?? :: decides what system command to use to clear the screen.

sub get_committer_list - err, smart-matching, unary =

• err is the low precedence form of // (S03). // is especially useful as

  	$x //= $y;
  	

• To summarize, || and or relate to truth, while // and err relate to definedness.
• Next, we use smart matching, ~~ (S04 - belongs in S03), to skip all of the lines from the beginning of the file which have something other than whitespace.
• we use the unary = to perform a readline operation on the filehandle.

sub pick_committer - junctions

incfile 'p6.sub_pick_committer'

sub draw_board - for, string concatenation

incfile 'p6.sub_draw_board';
• We loop over the numbers which are the indices to the elements of the array @letters by forcing the array into numerical context:

      for (0 .. (+@letters - 1)) -> $i { 
  	

• Now, ~= might throw you. You Perl 5'ers are seeing the regexp matching operator in reverse. But what you should be seeing is the Perl 6 string concatenation operator (~) followed by an equal sign. Which therefore means that

    $output ~= @letters[$i];  
  	

  translates to:

    $output = $output ~ @letters[$i] ; 
  	

  sub has_won - grep with adverbial block

  incfile 'p6.has_won';
  • Methods with arguments require parens. However, the block to grep isn't really an argument. It's describing the manner in which the array will be grepped... that's an adverb to grep.
  • So, why are the parens required on methods? Take the following if statements:

    if @foo.shift { ... }
    
    if @foo.grep { ... }   # grep doesn't get the block
    	

    To make things clear, methods without parens are assumed to take no arguments. In order to pass a block to the above grep, you either need to use @foo.grep({ $^a <=> $^b}) or the adverbial colon:

    if @foo.grep:{$^a <=> $^b} { ... }
    	

  • Many thanks to Ashley Winters for his explanation of this

  sub guess()

  incfile 'p6.sub_guess';

  sub draw_if_greater_than - constants, ternary operator

  sub draw_if_greater_than (Str $char, Int $num) returns Bool { 
      ($number_of_bad_guesses >= $num) ?? $char :: ' ';
      

  The character for blank should be a constant, e.g.:

  	 my ($BLANK) is constant = ' ';
  

  but it is not implemented yet.

  sub draw_hangman - function interpolation

  incfile 'p6.sub_draw_hangman'

  main loop - new repeat operator

  "x" in p5 is now "xx" in p6

    @solution = ('' xx +@letters); 
      

  The Whole Program

  incfile 'hangman.p6'

  Credits

  • author: Terrence Brannon
  • Substantial #perl6 help from mauke, ninereaons, revdiablo, autrijus, stevan
  • perl6-language help from Ashley Winters