Built-in Values

Every Whim value has a runtime type. A declaration can state which values it accepts. Whim checks that rule when the program reaches the boundary.

Scalar values

Whim has five scalar value kinds.

Integers and floats stay distinct:

assert!(1 is int);
assert!(1.0 is float);
assert!(1 != 1.0);

Strings hold bytes, not a promise of valid UTF-8. The source file is UTF-8, but a string may contain any byte through escapes, file reads, sockets, or binary decoding.

Arrays

Whim has three array forms:

array<K, V> accepts a tuple, vec, or dict whose keys and values fit K and V.

$pair = ('Ada', 36);
$names = vec['Ada', 'Grace'];
$scores = dict['Ada' => 10, 'Grace' => 12];

assert!($pair is (string, int));
assert!($names is vec<string>);
assert!($scores is dict<string, int>);

The collections chapter covers their syntax and update rules.

Objects and callables

object accepts any class instance. A class or interface name accepts objects of that class or its subtypes.

fn(A, B): R accepts a callable with two parameters and result R:

function apply(fn(int): int $operation, int $value): int {
  return $operation($value);
}

$double = fn(int $value): int => $value * 2;
assert!(apply($double, 21) == 42);

classname<T> accepts a class name whose instances satisfy T.

Wide and empty types

mixed accepts every value. !never also means every value.

never accepts no value. A function with return type never cannot return. It must throw, exit, or keep running.

void is valid only as a function or method return. Such a callable returns no value. You cannot use void for a parameter or property.

Literal types

A scalar value may also act as a type:

function choose('yes'|'no' $answer): bool {
  return $answer == 'yes';
}

assert!(choose('yes'));

true, 42, and 'yes' each describe one value. Literal types make unions, ranges, enum cases, and constants precise.

Conditions

Conditions must be bool. Whim has no truthy or falsy conversion:

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

Write the test you mean:

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

This rule also applies to while, do ... while, &&, ||, &&=, and ||=.