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============================================================================

You know how double-quoted strings interpolate variables?

    my $name = "Alice";
    print "Hello, $name!";    # Hello, Alice!

But what about expressions? Math? Function calls?

    print "Sum: $x + $y";     # Sum: 5 + 3 (not 8!)

Enter the babycart operator:

    @{[ ]}

Five characters that let you interpolate ANY expression in a string.

============================================================================

PART 1: THE TRICK
-----------------

    my $x = 5;
    my $y = 3;

    print "Sum: @{[ $x + $y ]}";    # Sum: 8

The expression inside @{[ ]} gets evaluated and interpolated.

Works with anything:

    print "Time: @{[ scalar localtime ]}";
    print "Random: @{[ int(rand(100)) ]}";
    print "Upper: @{[ uc('hello') ]}";

============================================================================

PART 2: HOW IT WORKS
--------------------

Break it down from the inside out:

    @{[ EXPRESSION ]}

    [ EXPRESSION ]     Anonymous array reference containing EXPRESSION
    @{ ... }           Dereference that array reference

The expression is evaluated in list context, wrapped in an anonymous
array, then immediately dereferenced for interpolation.

It's a weird little dance, but it works.

          .--.
         |o_o |
         |:_/ |
        //   \ \
       (|     | )
      /'\_   _/`\
      \___)=(___/

============================================================================

PART 3: WHY THE NAME
--------------------

Look at the operator from the side:

    @{[ ]}

The @ is a person pushing a shopping cart []. Inside the cart is your
expression, going along for the ride.

It's called babycart because... there's a baby (your expression)
riding in the cart. Perl naming conventions are weird.

Also called the "pram" operator in British Perl circles.

============================================================================

PART 4: MATH IN STRINGS
-----------------------

The classic use case - calculations inside strings:

    my $price = 19.99;
    my $qty = 3;
    my $tax_rate = 0.13;

    print "Subtotal: @{[ $price * $qty ]}\n";
    print "Tax: @{[ $price * $qty * $tax_rate ]}\n";
    print "Total: @{[ $price * $qty * (1 + $tax_rate) ]}\n";

Output:

    Subtotal: 59.97
    Tax: 7.7961
    Total: 67.7661

No temporary variables needed.

============================================================================

PART 5: FUNCTION CALLS
----------------------

Call any function and interpolate the result:

    print "PWD: @{[ `pwd` ]}";
    print "Files: @{[ scalar(`ls | wc -l`) ]}";
    print "Date: @{[ scalar localtime ]}";
    print "Name: @{[ (getpwuid($<))[0] ]}";

Backticks, builtins, anything goes.

============================================================================

PART 6: COMPLEX EXPRESSIONS
---------------------------

You can go nuts:

    my @nums = (1, 5, 3, 9, 2);

    print "Sorted: @{[ sort { $a <=> $b } @nums ]}\n";
    print "Max: @{[ (sort { $b <=> $a } @nums)[0] ]}\n";
    print "Sum: @{[ do { my $s; $s += $_ for @nums; $s } ]}\n";

Output:

    Sorted: 1 2 3 5 9
    Max: 9
    Sum: 20

The do{} block lets you run multiple statements.

============================================================================

PART 7: CONDITIONALS
--------------------

Ternary operators work great:

    my $count = 0;
    print "You have @{[ $count || 'no' ]} items\n";
    # You have no items

    $count = 5;
    print "You have @{[ $count == 1 ? 'item' : 'items' ]}\n";
    # You have items

Dynamic pluralization:

    print "Found @{[ $n ]} file@{[ $n == 1 ? '' : 's' ]}\n";

============================================================================

PART 8: HEREDOCS
----------------

Babycart shines in heredocs:

    my $name = "Alice";
    my $items = 5;
    my $total = 49.95;

    print <<"END";
    Dear @{[ uc $name ]},

    Your order of @{[ $items ]} items totaling \$@{[ sprintf "%.2f", $total ]}
    has been shipped.

    Sincerely,
    @{[ scalar localtime ]}
    END

Output:

    Dear ALICE,

    Your order of 5 items totaling $49.95
    has been shipped.

    Sincerely,
    Mon Jan  6 14:35:22 2025

============================================================================

PART 9: GOTCHAS
---------------

List context inside means arrays expand:

    my @things = qw(one two three);
    print "Things: @{[ @things ]}";
    # Things: one two three

If you want the count:

    print "Count: @{[ scalar @things ]}";
    # Count: 3

Or use the Venus operator:

    print "Count: @{[ 0 + @things ]}";
    # Count: 3

============================================================================

PART 10: VS CONCATENATION
-------------------------

You could always use concatenation:

    print "Sum: " . ($x + $y) . "\n";

But babycart keeps everything in one string:

    print "Sum: @{[ $x + $y ]}\n";

In heredocs and long strings, babycart is cleaner. In simple cases,
concatenation might be more readable.

Your call. Both work.

============================================================================

PART 11: SPRINTF TRICK
----------------------

For formatted numbers:

    my $pi = 3.14159265359;
    print "Pi: @{[ sprintf '%.2f', $pi ]}\n";
    # Pi: 3.14

    my $bytes = 1536;
    print "Size: @{[ sprintf '%.1f KB', $bytes/1024 ]}\n";
    # Size: 1.5 KB

Embedding sprintf in babycart is a common pattern.

============================================================================

PART 12: IN ONE-LINERS
----------------------

Print line numbers with content:

    perl -lne 'print "@{[$.]} $_"' file.txt

Pad numbers:

    perl -le 'print "Num: @{[ sprintf q(%05d), $_ ]}" for 1..5'

Output:

    Num: 00001
    Num: 00002
    Num: 00003
    Num: 00004
    Num: 00005

============================================================================

                    @{[  ]}
                      ||
                    [ baby ]
                    /______\
                   O        O

         Your expression, along for the ride

============================================================================

japh.codes