Functions

Functions are the primary way to organize reusable code in Zymba. Zymba supports named functions, anonymous functions assigned to variables, closures that capture outer scope, and higher-order functions that accept or return other functions.

The key thing to understand upfront is scope isolation: Zymba functions have their own scope and cannot access variables from the surrounding context unless those variables are passed as parameters or explicitly captured with a use clause.

Scope rules

Function scope is isolated

Variables declared outside a function are not accessible inside:

ZYMBA

$x = 42;

function $test() {
    return $x; // $x is not available — returns null
}

echo $test(); // (empty)

Variables don't leak out

Variables declared inside a function don't affect the outer scope:

ZYMBA

$x = 42;

function $test() {
    $x = 99; // Local $x, different from outer $x
}

$test();
echo $x; // 42 (unchanged)

Accessing outer variables

Two options for using outer variables inside a function:

1. Pass as parameters (preferred for named functions):

ZYMBA

function $format($value, $currency) {
    return $currency . @Number.format($value, 2);
}
echo $format(19.99, "$"); // "$19.99"

2. Capture with use (closures only):

ZYMBA

$currency = "$";
$format = function($value) use ($currency) {
    return $currency . @Number.format($value, 2);
};
echo $format(19.99); // "$19.99"

Function introspection

The @Function class provides reflection capabilities:

ZYMBA

$fn = function($a, $b, $c = 10) {
    return $a + $b + $c;
};

echo @Function.countParameters($fn);  // 3
echo @Function.isUserDefined($fn);    // true
echo @Function.isVariadic($fn);       // false

$names = @Function.listParameterNames($fn);
// ["a", "b", "c"]

Method	Description
@Function.call($fn, $bind, ...$args)	Call a function with explicit binding
@Function.countParameters($fn)	Number of parameters
@Function.isInternal($fn)	Whether the function is built-in
@Function.isUserDefined($fn)	Whether the function is user-defined
@Function.isVariadic($fn)	Whether the function uses ...
@Function.listParameterNames($fn)	Array of parameter name strings
@Function.listParameters($fn)	Array of parameter details

See also

• Named Functions — declaration, defaults, variadic parameters, return values
• Closures — anonymous functions, use clause, higher-order functions, patterns