Your First Program

Create hello.whim:

write_line!('Hello, Whim!');

Run it:

whim hello.whim

Whim runs statements at file scope. You do not need a main function.

Variables

A variable starts with $. Assignment creates it:

$language = 'Whim';
$year = 2026;

write_line!($language . ' ' . $year);

Whim infers the variable’s type from its value. A later assignment may change that type:

$value = 10;
$value = 'ten';

assert!($value is string);

Use == and != for equality. Conditions must produce bool:

$name = 'Ada';
if ($name != '') {
  write_line!('Hello, ' . $name);
}

if ($name) is an error. Whim does not turn strings, numbers, arrays, or null into booleans.

A function declares each parameter and its return type:

function square(int $number): int {
  return $number * $number;
}

assert!(square(9) == 81);

Whim checks the argument before the call and checks the result before it returns to the caller.

Use a fully qualified name or import a symbol:

use Whim\Str;

$parts = Str\split('one,two,three', ',');
assert!(length!($parts) == 3);

One use form imports classes, interfaces, enums, functions, constants, aliases, and newtypes.

From a project with a whim.toml, format every project source:

whim fmt

You may instead name one file or directory:

whim fmt hello.whim
whim fmt src

Use --check when you want a nonzero exit status instead of an edit:

whim fmt --check

The next chapter builds a program with files, loops, and a dict.