Closures can be used to consume items from a thing, list, tuple or set. They are also used by procedures where they get the role of a function.

Closure can be stored in a collection or assigned to a variable.

A closure starts with a |, then takes optional arguments and a | to close, followed by a statement. The most simple closure is ||nil which is a closure without arguments and returns the value nil when called.

More complex closures are also possible, check the last example below.


Method Description
call Call the closure with optional arguments.
doc Returns the doc string of the closure.

It is not possible to use closures with recursion, for example: a = ||.map(a); .map(a);
…will raise operation_err() (closures cannot be used recursively)

Doc string

Doc strings can be set for closures. This is especially useful for when closures are used inside a procedure but are not common when closures are used for other purposes.

Usually, a doc string is just a normal string on top of a block in the closure.

For example:

|| {
    "this is a doc string.";

It is common to wrap a block scope within one or more functions. When this is the case, the doc string will be read from the the first argument, only if the first non-function argument contains a block scope with a doc string.

For example, this closure contains a block scope wrapped with return and wse:

|| return(wse({
    "this is still a doc string, even while wrapped using `return` and `wse`.";
}), 2);


This code uses a simple closure together with map and call:

// create a simple closure which just adds one to a given value
add_one = |x| x+1;

// use the closure in a `map` function
map_result = [1, 2, 3].map(add_one);

// use the closure as a function call
call_result = add_one(41);

// return the result values
[map_result, call_result];

Return value in JSON format


Like explained, closures can accept multiple arguments and may contain a block scope instead of just a single line statement. Here is an example:

|name, age| {
    "Returns a thing with properties `name`, `age` and `time`.";

    assert(isstr(name) && name.len());
    assert(isint(age) && age >= 0);

    // this is the last statement so it will be the return value
        name: name,
        age: age,
        time: now()