Control Flow

Conditionals, loops, and exception handling.

Conditionals

If / Elsif / Else

my int $x = 10;

if ($x > 10) {
    say("Greater than 10");
} elsif ($x == 10) {
    say("Equal to 10");
} else {
    say("Less than 10");
}

Unless

unless is the opposite of if:

my int $logged_in = 0;

unless ($logged_in) {
    say("Please log in");
}

# Equivalent to:
if (!$logged_in) {
    say("Please log in");
}

Ternary Operator

my int $age = 20;
my str $status = $age >= 18 ? "adult" : "minor";
say($status);  # "adult"

Loops

While Loop

my int $i = 0;
while ($i < 5) {
    say($i);
    $i++;
}

For Loop

for (my int $i = 0; $i < 5; $i++) {
    say("i = " . $i);
}

Foreach Loop

Iterate over arrays:

my array @fruits = ["apple", "banana", "cherry"];

# With type declaration
foreach my str $fruit (@fruits) {
    say($fruit);
}

# Without type (uses existing variable)
my str $item;
foreach $item (@fruits) {
    say($item);
}

# "for" works like "foreach" with arrays
for my str $fruit (@fruits) {
    say($fruit);
}

Increment/Decrement

my int $x = 5;

$x++;        # Post-increment: returns 5, then x becomes 6
++$x;        # Pre-increment: x becomes 7, returns 7
$x--;        # Post-decrement: returns 7, then x becomes 6
--$x;        # Pre-decrement: x becomes 5, returns 5

# Often used in loops
my int $i = 0;
while ($i < 10) {
    say($i++);  # Print then increment
}

Loop Control

for (my int $i = 0; $i < 10; $i++) {
    if ($i == 3) {
        next;      # Skip to next iteration
    }
    if ($i == 7) {
        last;      # Exit loop
    }
    say($i);
}
# Output: 0, 1, 2, 4, 5, 6

Labeled Loops

Labels allow breaking out of nested loops:

OUTER: for (my int $i = 0; $i < 5; $i++) {
    INNER: for (my int $j = 0; $j < 5; $j++) {
        if ($j == 2) {
            next INNER;   # Skip to next inner iteration
        }
        if ($i == 3) {
            last OUTER;   # Exit both loops
        }
        say("i=" . $i . " j=" . $j);
    }
}

Exception Handling

Try / Catch / Throw

func divide(int $a, int $b) int {
    if ($b == 0) {
        throw "Division by zero!";
    }
    return $a / $b;
}

func main() int {
    try {
        my int $result = divide(10, 0);
        say("Result: " . $result);
    } catch ($e) {
        say("Error: " . $e);
    }
    say("Program continues...");
    return 0;
}

Nested Try/Catch

try {
    try {
        throw "Inner error";
    } catch ($e) {
        say("Caught inner: " . $e);
        throw "Re-throwing";  # Re-throw or throw new
    }
} catch ($e) {
    say("Caught outer: " . $e);
}

Goto and Labels

For exceptional control flow (use sparingly):

func main() int {
    my int $i = 0;

start:
    say($i);
    $i++;
    if ($i < 5) {
        goto start;
    }

    say("Done");
    return 0;
}

Pattern Matching

Use regex in conditionals:

my str $input = "hello123";

if ($input =~ /[0-9]+/) {
    say("Contains numbers");
}

if ($input !~ /^[0-9]+$/) {
    say("Not purely numeric");
}

# Case-insensitive match
if ($input =~ /HELLO/i) {
    say("Found hello (case-insensitive)");
}

Switch Statement

Use switch for multi-way branching:

my int $day = 3;

switch ($day) {
    case 1 {
        say("Monday");
    }
    case 2 {
        say("Tuesday");
    }
    case 3 {
        say("Wednesday");
    }
    default {
        say("Other day");
    }
}

Switch with Strings

my str $color = "red";

switch ($color) {
    case "red" {
        say("Stop");
    }
    case "yellow" {
        say("Caution");
    }
    case "green" {
        say("Go");
    }
    default {
        say("Unknown signal");
    }
}

Alternative: Hash Dispatch

For dynamic dispatch or function tables, hashes work well:

my hash %day_names = {
    "Mon" => "Monday",
    "Tue" => "Tuesday",
    "Wed" => "Wednesday"
};

my str $day = "Mon";
if (exists(%day_names, $day)) {
    say($day_names{$day});
} else {
    say("Unknown day");
}

Short-Circuit Evaluation

# && and || short-circuit
my int $x = 0;

# Second expression not evaluated if first is false
$x && say("x is true");

# Second expression not evaluated if first is true
$x || say("x is false");

# Use for default values
my str $name = "";
my str $display = $name || "Anonymous";