Как выполнить машинный код (изучение блока)

Perl

• Смешанное использование символов

  my @array = ( 1, 2, 3 );
  my $array = [ 4, 5, 6 ];
  
  my $one  = $array[0]; # not @array[0], you would get the length instead
  my $four = $array->[0]; # definitely not $array[0]
  
  my( $two,  $three ) = @array[1,2];
  my( $five, $six   ) = @$array[1,2]; # coerce to array first
  
  my $length_a = @array;
  my $length_s = @$array;
  
  my $ref_a = \@array;
  my $ref_s = $array;
  

  • Например, ни один из них не то же:

    $array[0]   # First element of @array
    @array[0]   # Slice of only the First element of @array
    %array[0]   # Syntax error
    $array->[0] # First element of an array referenced by $array
    @array->[0] # Deprecated first element of @array
    %array->[0] # Invalid reference
    $array{0}   # Element of %array referenced by string '0'
    @array{0}   # Slice of only one element of %array referenced by string '0'
    %array{0}   # Syntax error
    $array->{0} # Element of a hash referenced by $array
    @array->{0} # Invalid reference
    %array->{0} # Deprecated Element of %array referenced by string '0'
    

  В Perl6 это записано:

  my @array = ( 1, 2, 3 );
  my $array = [ 4, 5, 6 ];
  
  my $one  = @array[0];
  my $four = $array[0]; # $array.[0]
  
  my( $two,  $three ) = @array[1,2];
  my( $five, $six   ) = $array[1,2];
  
  my $length_a = @array.length;
  my $length_s = $array.length;
  
  my $ref_a = @array;
  my $ref_s = $array;
  

• Отсутствие истинного OO

  package my_object;
  # fake constructor
  sub new{ bless {}, $_[0] }
  # fake properties/attributes
  sub var_a{
    my $self = shift @_;
    $self->{'var_a'} = $_[0] if @_;
    $self->{'var_a'}
  }
  

  В Perl6 это записано:

  class Dog is Mammal {
      has $.name = "fido";
      has $.tail is rw;
      has @.legs;
      has $!brain;
      method doit ($a, $b, $c) { ... }
      ...
  }
  

• Плохо разработанные regex функции

  /(?=regexp)/;           # look ahead
  /(?<=fixed-regexp)/;    # look behind
  /(?!regexp)/;           # negative look ahead
  /(?regexp)/;           # independent sub expression
  /(capture)/;            # simple capture
  /(?:don't capture)/;    # non-capturing group
  /(?regexp)/;      # named capture
  /[A-Z]/;                # character class
  /[^A-Z]/;               # inverted character class
  # '-' would have to be the first or last element in
  # the character class to include it in the match
  # without escaping it
  /(?(condition)yes-regexp)/;
  /(?(condition)yes-regexp|no-regexp)/;
  /\b\s*\b/;              # almost matches Perl6's 
  /(?{ print "hi\n" })/;  # run perl code
  

  В Perl6 это записано:

  /   /;   # lookahead
  /    /;   # lookbehind
  / regexp :: pattern  /;   # backtracking control
  / ( capture )        /;   # simple capture
  / $=[ regexp ] /;   # named capture
  / [ don't capture ]  /;   # non-capturing group
  / <[A..Z]>           /;   # character class
  / <-[A..Z]>          /;   # inverted character class
  # you don't generally use '.' in a character class anyway
  /                /;   # Smart whitespace match
  / { say 'hi' }       /;   # run perl code
  

• Отсутствие нескольких диспетчеризирует

  sub f(   int $i ){ ... }  # err
  sub f( float $i ){ ... }  # err
  sub f($){ ... } # occasionally useful
  

  В Perl6 это записано:

  multi sub f( int $i ){ ... }
  multi sub f( num $i ){ ... }
  multi sub f( $i where $i == 0 ){ ... }
  multi sub f(     $i ){ ... } # everything else
  

• Плохая перегрузка Оператора

  package my_object;
  use overload
    '+' => \&add,
    ...
  ;
  

  В Perl6 это записано:

  multi sub infix:<+> (Us $us, Them $them) |
                      (Them $them, Us $us) { ... }