use strict;
use warnings;
use List::Util qw(shuffle);
use Term::ReadKey;

my $goodcount = 0;
my %riddle    = (
  'A ... has a changeable length.'                => 'a',
  'A ... does not have changeable length.'        => 'l',
  'A ... is something you can push or pop.'       => 'a',
  'A ... is a set of values.'                     => 'l',
  'Some people say a ... is a value.'             => 'l',
  'Some people say a ... is a variable.'          => 'a',
  'A subroutine is passed a ... '                 => 'l',
  'A subroutine returns a ... '                   => 'l',
  'You put things into ... context.'              => 'l',
  'You initialize a ... with a list.'             => 'a',
  'You initialize an array with a ... '           => 'l',
  'You "foreach()" across a ... '                 => 'l',
  'A "@" variable is a ... '                      => 'a',
  'An anonymous array is a ... '                  => 'a',
  'A ... in scalar context behaves like the number of elements in it.'
                                                  => 'a',
  'Subroutines access their arguments through the ... @_.'
                                                  => 'a',
  '"push"/"pop"/"shift" only work on a ... '      => 'a',
  'There is no such thing as a ... in scalar context.'
                                                  => 'l',
  '$scalar = (2, 5, 7, 9); There never was a ... there at all.'
                                                  => 'l',
);


#
# intro:
#

system("clear");
print 'Read the following FAQ:', $/, $/;
print <DATA>;

print 'Now start practicing.';
print ' Don\'t hesitate to re-read the FAQ if needed.', $/;
print 'Answer each of the ', scalar keys %riddle,
  ' questions with \'l\' (list) or \'a\' (array).',
  $/, $/;

ReadMode 'cbreak';    # no enter pressing


#
# loop through the questions:
#

for my $question ( shuffle keys %riddle ) {
    print $question, ' ';
    my $answer = ReadKey(0);
    if ( $answer eq $riddle{$question} ) {
        print $answer, ' RIGHT', $/;
        $goodcount++;
    }
    else {
        print $answer, ' WRONG', $/;
    }
}


#
# the result:
#

print $/;
if ( $goodcount / scalar keys %riddle > 0.6 ) {    
    # being generous with that 0.6
    print 'Wel done!', $/;
}
print 'Got ', $goodcount, ' out of ', 
      scalar keys %riddle, ' good.', $/;


      
__DATA__
4.39: What is the difference between a list and an array?

    An array has a changeable length. A list does not. An 
    array is something you can push or pop, while a list 
    is a set of values. Some people make the distinction 
    that a list is a value while an array is a variable.
    
    Subroutines are passed and return lists, you put things
    into list context, you initialize arrays with lists, 
    and you "foreach()" across a list. "@" variables are 
    arrays, anonymous arrays are arrays, arrays in scalar 
    context behave like the number of elements in them, 
    subroutines access their arguments through the array 
    @_, and "push"/"pop"/"shift" only work on arrays.

    As a side note, there's no such thing as a list in 
    scalar context. When you say

            $scalar = (2, 5, 7, 9);

    you're using the comma operator in scalar context, so
    it uses the scalar comma operator. There never was a 
    list there at all! This causes the last value to be 
    returned: 9.
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