If we apply operation X to a variable of type Y, 
    we get a variable of type Z.

##</code><code>##

    X(Y) : Z

##</code><code>##

    $GLOBAL  = "static";
    $LOCAL   = "dynamic";
    $LEXICAL = "lexical";
    
    sub show_evaluation_context {
        printf (
            "evaluation context:  %s \n",
            join (',', ($GLOBAL, $LOCAL, $LEXICAL))
        );
    }
    
    sub global_scope {
        printf (
            "global scope:        %s \n",
            join (',', ($GLOBAL, $LOCAL, $LEXICAL))
        );
        show_evaluation_context();
    }
    
    global_scope();

##</code><code>##

    global scope:        static,dynamic,lexical 
    evaluation context:  static,dynamic,lexical

##</code><code>##

    sub local_scope {
        local ($LOCAL) = "-------";
        printf (
            "local scope:         %s \n",
            join (',', ($GLOBAL, $LOCAL, $LEXICAL))
        );
        show_evaluation_context();
    }
    local_scope();
    print "\n";
    print "but outside local_scope(), we still have:\n";
    show_evaluation_context();

##</code><code>##

    local scope:         static,-------,lexical 
    evaluation context:  static,-------,lexical 
    
    but outside local_scope(), we still have:
    evaluation context:  static,dynamic,lexical 

##</code><code>##

    sub lexical_scope {
        my ($LEXICAL) = "-------";
        printf (
            "lexical scope:       %s \n",
            join (',', ($GLOBAL, $LOCAL, $LEXICAL))
        );
        show_evaluation_context();
    }
    
    sub local_override {
        local ($LEXICAL) = 'DYNAMICALLY RE-BOUND VALUE';
        lexical_scope();
    }
    
    local_override();
    print "\n";
    lexical_scope();

##</code><code>##

    lexical scope:       static,dynamic,------- 
    evaluation context:  static,dynamic,DYNAMICALLY RE-BOUND VALUE 
    
    lexical scope:       static,dynamic,------- 
    evaluation context:  static,dynamic,lexical 

##</code><code>##

    package Foo;
    
    $VAR1 = "VAR1 in package 'Foo'.";
    
    package main;
    
    $VAR1 = "VAR1 in package 'main'.";
    $VAR2 = "VAR2 in package 'main'.";
    
    print $Foo::VAR1, "\n";
    print $VAR1, "\n";
    print $VAR2, "\n";

##</code><code>##

    VAR1 in package 'Foo'.
    VAR1 in package 'main'.
    VAR2 in package 'main'.

##</code><code>##

    my $total = 0;
    for $i (1..10) {
        $total += $i;
    }
    print $total, "\n";

##</code><code>##

    sub sum_of {
        my ($item, @list) = @_;
        return ((defined $item) ? $item + sum_of (@list) : 0);
    }
    print sum_of (1..10), "\n";